System of Linear Equations - Substitution

2x = 50

x = 25

x+y=40

25 + y = 40

40 - 25 = y

y = 15

multiply the second equation by 2

2(x+y) = 2(40)

2x+2y = 80

eliminate the first equation gives

2y = 30

y = 15

$\boxed{2x = 50}$

$\boxed{x + y = 40}$

$2(x + y) = 80$

$2x + 2y = 80$

$2y = 80 - 2x$

$2y = 80 - 50$

$2y = 30$

$\large y = \frac{30}{2}$

$\color{#20A900}\boxed{y = 15}$

Simplifying the first equation, we have $x = \frac{50}{2} = 25$ . Substituting $x=25$ into the second equation, we have $25 + y = 40$ $\Rightarrow y = 40 - 25 = 15$ .