Answer/Step-by-step explanation:
a. Diagonals of a rectangle are equal to each other. Therefore:
9x + 20 = 10x + 8
Collect like terms
9x - 10x = -20 + 8
-x = -12
Divide both sides by -1
x = 12
b. One of the properties of a rhombus is that, a diagonal of a rhombus bisects the angles of a rhombus. Therefore, this means that:
2x + 15 = 5x + 3
Collect like terms
2x - 5x = -15 + 3
-3x = -12
Divide both sides by -3
x = 4