
Given that the perimeter is 16ft and width is 5 ft,

Distribute 2:

Take away 10 from both sides:

Evaluate the right hand side:

Divide by 2 on both sides:

The percent is 145. That should be your answer
If the initial time was 60 seconds and 18 seconds have passed,

There would be 42 seconds left.
Personally I would take each ingredient/ 4, then subtract ur answer from the original. So 80g strawberry jelly, 6sponge fingers, 315 custard, 35 tinned fruit
The volume would be 5 because in order to find volume you need to divide mass over density. V=m/d