Question

Sistema
X+y=40
X/y=7/3

Answer 1

x=40-y

$\frac{x}{y}= \frac{7}{10} \\ \frac{40-y}{y}= \frac{7}{3} \\ 7y=3(40-y) \\ 7y+3y=120 \\ 10y=120 \\ y= \frac{120}{10} \\ y=12 \\ Substituindo \\ x=40-12 \\ x=28$

Answer 2

x + y = 40
x/y = 7/3 ______ x = 7y/3

substituindo na primeira equação
x + y = 40
7y/3 + y = 40

mmc (1,3) = 3

7y/3 + 3y/3 = 120/3
7y + 3y = 120
10y = 120
y = 120/10
y = 12

x + y = 40
x + 12 = 40
x = 40 - 12
x = 28