(x + 2/3) : 15/21 = 7/5
x + 2/3 = 7/5 × 15/21
x + 2/3 = 1
x = 1 - 2/3
x = 1/3
39/15 : (x - 1/6) = 13/15
x - 1/6 = 39/15 : 13/15
x - 1/6 = 3
x = 3 + 1/6
x = 18/6 + 1/6
x = 19/6
( x + 2/3 ) : 15/21 = 7/5
x+2/3=7/5×15/21
x+2/3=1
x=1-2/3=1/3.
39/15 : ( x - 1/6 ) = 13/15
x-1/6=39/15:13/15
x-1/6=3
x=3+1/6
x=18/6+1/6=19/6.