Ok, we know that there are 270 degrees in a triangle, so just add 49+57, the you'll get 106, 270-106=164. ANSWER: 164
A linear function is one whose formula can be written in the form
Ax + By = C where A, B, C are real numbers and A, B are not both 0. (This is standard form, too.)

"Cross multiply."

Subtract 12.

Subtract 2y.

This matches up with standard form with A = 3, B = -2, C = -20.
It's a linear function.
The second constraint is the same as the objective function, so your problem boils down to finding integer solutions to
.. 3x1 +5x2 = 36
There are 3 solutions. They are (x1, x2) = (12, 0), (7, 3), (2, 6)
The value of the objective function there is (obviously) 36.