The farmer

1 hour = 60 minutes

so, a tractor can plough 4 hectors in = $6 \times 60$ minutes .....................[6 hour =6 x 60 minutes =360 minutes]]

or, a tractor can plough 1 hector in = $\frac {360}{4}$ minutes =90 minutes

or, a tractor can plough 7 hectors in = $90 \times 7$ minutes =630 minutes

4 hectares in 6 hours, that's 1 hectare every 1.5 hours (6 divided by 4). 1.5 x 7 = 10.5 hours, 60 minutes in an hour so that's 630 minutes.