Question

................................. 3х+21=39х

Answer 1

3x + 21 = 39x
3x - 39x = -21
-36x = -21
x = 7/12

Answer 2

$3x+21=39x \ 21=39x-3x \ 21=36x \ x=frac{21}{36}=frac{7cdot 3}{12 cdot 3} = frac{7}{12}$