Substitution

3x-4y=-15 and 5x+y=-2

We can write the second equation as y = -2-5x   ......and substituting this into the first equation for y, we have

3x -4(-2-5x)  = -15   simplify

3x + 8 + 20x   = -15

23x + 8  = -15     subtract 8 from both sides

23x  = - 23          divide both sides by 23

x = -1      and y = -2 -5(-1)  =  -2 + 5  = 3

So (x, y)  = (-1, 3)