Hey there!
So, first, you need to rearrange the second equation so y is in front.
x+y=10
Subtract x.
y=10-x
Plug that in for y.
2x+3(10-x)=45
2x+30-3x= 45
Subtract 30 on both sides.
-x= 15
Divide by -1 on both sides.
x=-15.
I hope this helps!
~kaikers
