X=5 becuase if 7*3=21 then x*3=15 and 5 times 3 = 15
So the answer is 12
so i believe that 21 shrinks down to 7 and then you find what multiplication can make 7 to 21 and the answer is 3 because of 7*3=21
then you do the same to the other side which is 15 but instead you divide by 3 which gives you 5 so
x=5
