Answer:
36
Step-by-step explanation:
Objective: Find missing dimensions of the right triangle using the then subtract that area of the triangle from the rectangle's area.
Using the definition of a rectangle, the left vertical side measure is 7 and right vertical side is 6. So the missing legs of the triangle is 4 and 3.
Apply triangle formula, base x height divided by 2.

Area of rectangle is length x width so the area is

Subtract 6 from 42.

Again here we're using like terms
a) -2x² + 12x² = 10x² (they have the same term that's why I grouped them together)
-4x + 2x = -2x
13 - 25 = -12
So the final answer is 10x² - 2x -12
b) 7x² - (-7x²) = 7x² + 7x² or 14x²
4x - (-3x) = 4x + 3x or 7x
-26 - 15 = -41
The final answer to this one is 14x² + 7x - 41