Question

qual o valor de x na proporcao x/6=(x+3)/15 ?

Answer 1

$\frac{x}{6} = \frac{x+3}{15}$

Faça a proporção cruzada 

$15x = 6(x+3)$

$15x = 6x + 18$

$15x - 6x = 18$

$9x = 18$

$x= \frac{18}{9} = 2$