Had to search up word gradient since i didnt know what it meant LUL!
Equation of a line is y = mx + b
You have m, which is the gradient so all you need is b. To do this, sub in the point (2,-5) as x and y to get:
-5 = (5)(2) + b
and you get b equaling to -15
so your equation is y = 5x - 15
you can check this by subbing back in your x value and you should get the same y.