Hello from MrBillDoesMath!
Answer:
x = 10
Discussion:
A plane triangle contains 180 degrees. Adding the angles in the triangle shown in #8 gives
(4x + 7) + (3x + 13) + 90 = 180
Note the "right angle" shown in the triangle has been replaced by its 90 degree equivalent in the above equation.
Combining like terms gives
( 4x + 3x) + (7 + 13) + 90 = 180
7x + 20 + 90 = 180 => (subtract 90 from each side)
7x + 20 + 90 - 90 = 180 - 90 = 90 =>
7x +20 = 90 => (subtract 20 from each side)
7x + 20 -20 = 90 -20 =>
7x = 70 =>
x 70/7 =10.
Thank you,
MrB