Question

I need help,I need to use substitution but I don't know how

Answer 1

If $y=x+6$ and $y=-2x-3$, then you can replace $y$ in either equation with the equivalent expression given by the other equation. In this case, you have

$x+6=-2x-3$

and you can solve for $x$.

$x+2x+6-6=-2x+2x-3+6\implies3x=3\implies\dfrac{3x}3=\dfrac33\impliesx=1$

Then $y=1+6=7$.

For the second system, you can write

$5x-y=-5\implies 5x-5x-y=-5-5x\implies-y=-5-5x$

$\implies-(-y)=-(-5-5x)\implies y=5+5x$

Then substitute this into the second equation and you get

$3x-6(5+5x)=24\implies3x-30-30x=24\implies-27x-30+30=24+30$

$\implies-27x=54\implies x=2$

so that

$y=5+5(2)=15$