Question

a,b and c earn 300 a and c earn together 188 b and c earn 152 only c can earn?

Answer 1

This problem can be consider as a set of linear equations.

a, b and c earn 300.
i.e,    
        a + b + c = 300  -----------(i)
a and c earn together 188.
i.e,
       a + c = 188  -----------------(ii)
b and c earn together 152.
i.e,
       b + c = 152  -----------------(iii)
from equation (i) and (ii)
    (a + c) + b = 300
or, 188 + b = 300
or, b = 300 - 188 
or, b = 112
then,
     c =  152 -b
or, c = 152 - 112
or, c = 40
Therefore only c can earn up to 40.

Answer 2

A+C=188
B=112
C=40
A=148