What year-to-date contribution to sales ratio (C/S ratio) would be reported at the end of month 10?

The year-to-date results at the end of month 9 included sales revenue of $3,600,000 and variable costs of $2,100,000. During month 10, sales revenue was $450,000 and variable costs were $270,000.

What year-to-date contribution to sales ratio (C/S ratio) would be reported at the end of month 10?
A . 58,5%
B . 70,9%
C . 41,5%
D . 40,0%

Answer: A