Water expension in math

Answer credited to @Asafmen

We need a mass that will increase approximately by 10%, so roughly x to 1.1x.

If we look at the numbers, we will need to add 10% to them to obtain {}\frac {109}{110} %} %.

The only answer that will not exceed 40 dramatically is 36.7; 36.7+3.67= 40.3 (which is just about 40)- anything else would be greater than that. This makes the answer A.