Let size of cube = s
And % error of side = Δs/s * 100 = x (given)
Then volume = s3 = f(s)
So relative error of volume = Δ(s3) /s * 100 which can be rewritten as :
= 3 (Δs/s) * 100 [Using exponent rule of finding errors]
= 3x
Hence the correct answer is 3x and hence B) is the correct option