Square garden is 12 feet long on each side. put a post at each corner and every 3 feet on each side. how many posts total?

As it is a square all sides are equal so all sides are 12 feet long.

how many posts on one side?

First we find out how many lengths of 3 we have for 1 side:
12  / 3 = 4
And then multiply this by the amount of sides
4 * 4 = 16

We need 16 posts

1 - 1 - 1 - 1 - 1
1                    1
1                    1
1                    1
1 - 1 - 1 - 1 - 1

Answer is 16. Workings in the attachment below.

Height of mound = 794 ft

Step-by-step explanation:

To illustrate the angle of elevation and distance, i have drawn it and attached below.

Now, from my diagram;

h = the height of the mound

At his first point of his trip to the foot of the mound, the angle of elevation is 40°, while the horizontal distance to the foot of the mound is "X"

So, by triangle definition,

tan(40°) = h/x

And so;

h = x tan40

h = 0.8391x  - - - - (eq 1)

At his second point of the trip to the foot of the mound, Joe is now,

"(x - 450) ft" from the foot of the mound.

Thus, his angle of elevation is 40 + 18 = 58°.

So, by triangle definition,

tan(58°) = h/(x - 450)

h = (x - 450)•(tan(58°))

h = 1.6003(x - 450)

h = 1.6003x - 720.135   - - - - -(eq2)

To get the height(h) of the mound, let's equate (eq1) to (eq2).

0.8391x = 1.6003x - 720.135

1.6003x - 0.8391x = 720.135

0.7612x = 720.135

x = 720.135/0.7612

x = 946.0523 ft

Let's put this value for x in eq (1);

h = 0.8391 x 946.0523 = 793.83 ft ≈ 794ft