Cerenity and Jas rented a jet ski for an afternoon. The rental fee for

Ans: C

lets say for first hour the rate is x and for additional hours rate is y (per hr) and given x>y
also given x+ty= 16.50 where (t+1) will be the total time for which they rented the ski.
(Edited after pointed out by @Priyanka8793)
stat 1: for first two hrs x+y=10.50 but we dont know the value of x and y (Not Suffi)

stat 2: 3y = 9 here we know the y but not the x (not Suffi)
Detailed: as it is calculated that for additional hours rate is $3/hr. after deducting the charge for the last three hour ride we are left with $7.50 from $16.50 given in question stem.
Possibility 1) first hour price is $7.50 and rest 3 hrs total $9 = $16.50 for 4 hrs
Possibility 2) first hour price is $4.5 and rest 4 hrs = $12 = $16.50 for 5 hrs.
B alone not sufficient..

together we can find x and y and then put it in the given (x+ty to get the t) thus we can get the t+1 (suffi)

Ans: C