Ihave solving systems of equations using substitution, and sometimes i have equations like this: 12x-5y=-20y=x+4and then stuff like this: 2x+7y=3x=-4yit's kind of hard to know how to do a lot of different equations for one topic, could someone show me how to do all the different kinds

For systems of equations try using graphing, substitution, and elimination. For example
{2x+7y=3}
{x=-4y}
You should first look at if you have a variable that can be substituted (using substitution) and in this case we do! you plug in the x into 2x meaning 2(-4y)+7y=3
1) distribute -8y+7y=3
2) combine like terms in this case -8y+7y= -1y
3) solve -1y=3
y=-3
so currently our solution is (0,-3)
now we solve for x.
we plug our solved variable (y) into 7y
7(-3) and our equation looks like this
2x+7(-3)=3
1) distribute 7(-3)=-21
2) rewrite then solve 2x+(-21)=3
3) isolate variable -21+21 & 3+21
4) 2x=24
5) solve 2/24 = 12
Meaning our solution is (12,-3)
This is how to solve by substitution.