What is 40% of 85? (with an explanation)

 32

Step-by-step explanation: 0.4 x 80=32

you change 40 to a decimal with is 0.4 time 80=32

34

Step-by-step explanation:

X is 12

Its kinda hard to explain but let me put it this way
If you can translate each of the fractions to have the same denomenator then it makes things a lot easier.

First you translate the equation into 9/12x - 4/12x + 10/12x = 12/12x + 3

Then subtract 12/12x from both sides to get 

9/12x - 4/12x + 10/12x - 12/12x = 3

Subtract 9/12x -4/12x = 5/12x

Then add 5/12x to 10/12x = 15/12x 

Then subtract 15/12x - 12/12x = 3/12x 

So you should get 3/12x = 3

which is 1/4x = 3 

Multiply both sides by 4 and you get 

x = 12