You must find the relative rates of both workers...
T=f/3 and J=f/2 so if they work together to clear the field then:
ft/3+ft/2=f make all terms have a common denominator of 6
(2/2)(ft/3)+(3/3)(ft/2)=(6/6)f
2ft/6+3ft/6=6f/6 multiply both sides by 6
2ft+3ft=6f divide both sides by f
2t+3t=6 combine like terms on left side
5t=6 divide both sides by 5
t=6/5 hr
t=1 1/5 hr
t=1 hr 12 min