We know the slope is -6/5 so so far we have y = -6/5x + b. To find b substitute (-5, 3) into the equation and solve.
y = mx + b
3 = -6/5(-5) + b
3 = 6 + b
Use the subtraction property of equality to get rid of 6 and isolate b (subtract 6 from 6 to cancel it out and to 3).
-3 = b
The correct answer is y = -6/5x - 3