A rectangular garden is 12 feet across and 16 feet long. It is surrounded by a border of mulch that is a uniform width x. The maximum area for the garden, plus the border, is 285 square feet.

OK,

First, Get a rectangular prism.
Examples of rectangular prism include cereal box (best example) , your room, or just a box.

Now, look at the picture i attached. "It is going to be at the bottom of this answer" 
In the picture,
h = height
l = length
w = width

Now,
Measure the h, l, and w of your example of a rectangular prism. Again, the examples of rectangular prism include cereal box (best example) , your room, or just a box.
Now, 
Put no. 1 in your sheet of paper and write the value for the h, l, and w.

For example,
1>
    h = the value of h
     l =  the value of l
    w = the  value of w
Of course, DON'T FORGET TO WRITE THE UNITS. If you are using a ruler with a centimeter (cm) scale, then your units are going to be in cm, and if you are using a inch (in) scale, then your units are going to be in in.

Now,
For no. (2)I DIDN'T UNDERSTAND THE QUESTION!!!  So, i don't know how to do no. (2) and i am sorry for that.
But, don't write  I DIDN'T UNDERSTAND THE QUESTION!!! in your paper for no. (2) . Go to your teacher and ask her how to do no. (2).

Now,
We have,

We know,
P = 2 (l + w)
B = l * w

So,
PH + 2B can also be written as,

So,

Now, you just have to plug in the value of l, w, and h in the formula and then you will get the Surface area of the rectangular prism.
And, that will be the answer to no. (3) 

Now,
The volume of a prism = Bh
Where,
B = the area of the Base
h = the height of the prism

We know,
B = (l * w)

 So, we can write,
Bh = (l * w) h
So,
Volume of a rectangular prism = l x w x h

Now, plug in the value of l, w, and h and find the volume of your rectangular prism.
And, this will be the answer to no. (5)
 I REPEAT no. (5) not no. (4)


Now,
Scaling up by a factor of 10 (probably) means multiplying each dimension by 10.

So, For no.4
You are going to have to multiply the value of l, w and h by 10 and plug the new number into the surface area formula.

What i mean is shown right below this statement.

So,
For no.(4) and no.(4) only, 

Now, just plug in the value of l, w, and h and solve it.
This is going to be the answer for no.(4)

Now,
We have to do the same thing to volume like we did with the surface area. What i mean by that is we have to multiply the value of l, w, and h by 
So,

So,
Volume for no. 6 =  

Now, just plug in the value of l, w, and h and solve it.

And this is going to be the answer for no. (6)