Given,

29% of 725 = 60% of 315 + ?

It can be appoximated as

30% of  700 = 60% of 315 + ?

$= \frac{30}{100}\times 700=\frac{60}{100}\times 300+?$

 = 210=180+?

 = 210-180

 = 30

Hence, Option B is correct.