Easiest way to do this question is ratio method

First day + Second day : Third day : Total
3 : 1 : 4

Second day : Third day
1 : 4

Change the units for third day to the same number for both ratios by multiplication.

Smallest common multiple of 1 and 4 is just 4.

So,
First day + Second day : Third day : Total
3 : 1 : 4
↓×4
12 : 4 : 16

Second day : Third day
1 : 4

We can now say :
total = 16 units
third day = 4 units
second day = 1 unit
first + second day = 12 units

Therefore, first day = 12 units - 1 unit = 1 units


Required fraction for part (a) = 11/16

b)

11 units = 264

1 unit = 264 ÷ 11 = 24

Total = 16 units = 16 × 24 = 384

Amount collected = $384 × 5 = $1920