Answer:
it will take 20 weeks for Lorna to have the same money as her sister. here's how;
both of the sisters save 7 & 5 correspondingly each week.
for Lorna it is 60 + 7x (x is number of weeks)
for her sister it is 120 +5x
we set both equal and solve for x
60+ 7x = 120 +5x
bring the like terms together and solve, we get x = 20.
if you put 20 as x you can see that both sides will become equal.