Question

(5//7 - 2/3y) * 21 = 1

Answer 1

$frac{5}{7} - frac{2y}{3} = frac{1}{21}$
$frac{15-14y-1}{21} =0$
$14-14y=0$
y=1

Answer 2

((15y-14)/21y)*21=1
(15y-14)/y=1
15y-14=y
14y=14
y=1