Answer:
u = 7 OR u = 13
Explanation:
Using the zero property of multiplication, you know you have to make either u-7 or u-13 equal to zero. You get the two solutions from these two cases, where you make either of the equations equal to 0:
u - 7 = 0
Add 7 to both sides
u = 7
u - 13 = 0
Add 13 to both sides
u = 13
FINAL ANSWER: u = 7 OR u = 13