Question 1191291
r, the rate for just 1 tractor

Five tractor rate is  5r;  {{{5r*12=1}}}


For 3 tractors, x number of days.
{{{5r*12=3r*x=1}}}


{{{5*12=3x}}}


{{{x=(5*12)/3}}}


{{{highlight(x=20)}}}