The first tank hold 1088 - 5t gallons of water after t weeks, while the seocnd tank holds 1360 - 9t gallons after t weeks.
Both tanks hold the same amount of water when
1088 - 5t = 1360 - 9t
Solve for t :
4t = 272
t = 68
So the tanks will hold the same amount of water after 68 weeks.