Question 494362
r, work rate of each man
x, the unknown time for the 7 men
1, the amount of jobs


{{{system((4r)*14=1,(7r)*x=1)}}}


See, each expression on the left equals  to 1, so

{{{4*14*r=7*x*r}}}

{{{4*14=7*x}}}

{{{x=(4*14)/7}}}

{{{highlight(x=8)}}}