Find the solution to the following system by substitution.

Question

3x + y = 30

y = 3x

A. (5,15)

B. (0,30)

C. (10,30)

D. (10,0)

Answer 1

A is correct (5,15)

just at a glance, only A or C are possibly correct, the answer is (x,y) = (x,3x)

and only (5,15) and (10,30) have the y coordinate 3 times the x coordinate

3x + y = 30

3(5) + 15 = 30

15 = 3(5)

3x+y = 30

y= 3x

3x +3x = 30

6x =30

x= 30/6 = 5

y=3x = 3(5) = 15