three fourths multiplied by twelve over twenty one is the same as
(3/4) x (12/21)
First we can simplify the fraction 12/21 to become
12/21 = (4x3)/(3x7) = 4/7
So, (3/4) x (12/21) = (3/4) x (4/7)
So this can then become,
(3/4) x (4/7) = (3x4) / (4x7)
= 3/7