This is an easy question on application of algebra.
First, you should write down all the facts you know.
(P for Phil, L for Lia and C for Cam.)
P + L + C = 200.30
P = L + 12.80
C = 3L
Second, you should find common letter in those equations.
In this case, it's L.
So, you should subtitute P = L + 12.80 and C = 3L to P + L + C= 200.30.
Then you will get (L + 12.80) + L + 3L = 200.30
Third, then you can solve it using basic algebra.
(L + 12.80) + L + 3L = 200.30
= 5L + 12.80 = 200.30
= 5L = 187.50
= L = 37.5
Lia collected 37.5.
Fourth, You just subtitute L to other equations.
Then you will get C and P as well.
Hope it helped!