+154 This is a simple subsitution.
3x+4y=5
2x+5y=15
To do this it is easier to use the elimination method
I multiplied the formulas buy 2 and 3 respectively to make x the common one but it can be done the other way round with y.
Anyway...
(multiply by 2)
6x+8y=10
(multiply by 3)
6x+15y=45
cancel out the x's
You get: 7y=35
Therefore y=5
Now substitute the above into the original equation...
3x+20=5
3x=-15
x=-5
Proof: -10+25=15
