Hello from MrBillDoesMath!
Answer:
x = 7
Discussion:
The small and large triangles are similar by AAA, So the ratio of corresponding parts is the same:
(40 + 5) / 5 = (2x +3 + 10) /3 =>
45/5 = (2x + 13) /3 => 45/5 = 9; cross multiply by 3
9*3 = 2x + 13 => subtract 13 form both sides
9*3 - 13 = 2x =>
27 - 13 = 2x =>
14 = 2x =>
x = 7
Thank you,
MrB
