Question

Sendo r e s retas paralelas, o valor de x no caso da foto é?

A) 8
B) 6
C) 10
D) 12

Answer 1

$\frac{x+8}{21}=\frac8{12}\\ 12(x+8)=8\cdot21\\ 12x+96=168\\ 12x=168-96\\ 12x=72\ \ \ \ |:12\\ x=72:12\\ x=6 \ \to \ \boxed{B}$