Because you have to multiply 3 to the denominator and what ever you do to the denominator u have to do to the numerator so If u did 3 time 5 it would be 15 but if u do 5 time 2 it would be 10 not 12 because the unit rate fraction is 2/3 so u multiply 3 to each denominator and numerator since 2/3 is the unit rate fraction
