Create an equation to solve for x, then solve to find its value.

Answer:
Equation: x + 16 + 13 + x = 21 ; x = -4
Step-by-step explanation:
x + 16 + 13 + x = 21 (Given)
2x + 29 = 21 (Added like terms)
2x = -8 (Subtracted 29 on both sides)
x = -4 (Divided 2 on both sides)