Answer:
a. $70.
b $100.
c. 14 weeks.
Step-by-step explanation:
The interest per week is 10% of $50
= 0.1 * 50
= $5.
So if he pays it off
In 4 weeks he pays back 50 +4*5 = $70,
in 10 weeks he pays back 50 + 10*5 = $100.
When he owes $120 we have the equation:
50 + 5x = 120 where x = the number of weeks.
5x = 70
x = 14 weeks.