A, B, C, and D invest $s. B invests m times as much as A, C as much as A and B combined, and D as much as C and B combined. Determine the amount each invests.

Answers given with problem:

A: s / 3 + 4m

B: ms / 3 + 4m

C: s(1 + m) / 3 + 4m

D: s(1 + 2m) / 3 + 4m

How do I solve ?