# How do you solve x+3y=7, -x+4=7?

Mar 22, 2016

Since the second equation is only in $x$, we'll solve that first:

#### Explanation:

Subtract $4$ from both sides:
$- x + \cancel{4} - \cancel{4} = 7 - 4 \to$
$- x = 3 \to x = - 3$

Now substitute this $x$-value in the other equation:
$- 3 + 3 y = 7$
Add $3$ to both sides:
$\cancel{3} - \cancel{3} + 3 y = 7 + 3 \to$
$3 y = 10 \to y = \frac{10}{3} = 3 \frac{1}{3}$