Here, we have two equations involving two variables, x and y.
The question asks us to 'solve' the set of simultaneous equations.
Equivalently, it is asking us to
Rearrange equation into the form: y = mx + c
m = gradient
3x + 5y = 7
5y = -3x + 7
y = (-3/5)x + (7/5)
gradient = (-3/5)