Yes because if you multiple numerator and denominator of 3/4 by 10 then you would get 30 / 40.
Another way to look at is to notice that 30 = 3×10 and 40 = 4×10
So that's 30 / 40 = ( 3×10 ) / ( 4×10 ) = 3 / 4 because 10 was cancelled, therefore they are equivalent to each other.
