Question 5473
if y=4x, then substitute this into the second equation:
x+(y)=5
x+(4x)=5
5x=5
x=1

If x=1, then 
y=4*1 or 4
the solution set is verified by testing these numbers in the other equation:
x+y=5
1+4=5  this is true so the answer has one solution:
(1,4)

The answer is put into parentheses, because we are talking about a point on a graph - where do these two lines cross?  The answer is (1,4)