Substitution means making one formula equal to a variable in the second formula to plug it in, and elimination means the cancelling out of one variable in order to make it easy to solve.
1. x-4(-x+5)=10
x+4x-20=10
5x=30
x=6, plug in 6 into original equation, y=-1
2. -1(2x-5y=6)
2x+3y=-2 underlined means cancelled, so you add the rest up on each side
5y+3y=-6+-2
8y=-8
y=-1, plug in this value to original equation, x=.5
3. 2(x+5)=2x+10
2x+10=2x+10
Infinite solutions
4. y=4x-3
-4(y=x+6) underlined means cancelled
-3y=-27
y=9, plug into original, x=3
