Question 150567
Initially, 
(1) {{{w = (3/4)*m}}}
(2) {{{w + 12 = (6/7)*(m + 6)}}}
Substitute (1) in (2)
{{{(3/4)m + 12 = (6/7)*m + 36/7}}}
Multiply both sides by {{{28}}}
{{{21m + 12*28 = 24m + 4*36}}}
{{{21m + 336 = 24m + 144}}}
{{{3m = 192}}}
{{{m = 64}}}
And, since
{{{w = (3/4)*m}}}
{{{w = (3/4)*64}}}
{{{w = 48}}}
At first, there were 64 men and 48 women