Answer :
Given : Susie saves $4 on Friday.
And
Each day after that she saves twice as much as she saved the day before .
So,
Susie saves on Saturday = 2 ( 4 ) = $ 8
And
On Sunday she saves = 2 ( 8 ) = $ 16
Then Susie have total money on Sunday = $4 + $8 + $16 = $ 28 ( Ans )