If we rewrite the equation: y=-x+5, we get: x=5-y. If we substitute this value of x in y=3x+1, then we get: y=3(5-y)+1. Which after evaluation, we get: y=4. Since answer B is the only answer containing 4 as the y value, we come to the conclusion that B is the answer. But if you want to be 100% sure that that is the answer, substitute the y and x values in both of the equations and you will get the correct answer.
