I assume from the question is that sum of A, B and C will be 740

A = 1.25 * B (25% more of B)

B = 1.2 * C (20% more of C)

and C = X of 740

If you substitute Value of B in 1st equation.

A = 1.25*(1.2 * C) = 1.5 * C

sub. the value of A, B and C to sum to 740

1.5 * C + 1.2 * C + C = 740

3.7C = 740

so C is approx 200 which is 27% of 740