Distance truck travels, Dt = 120 mi.

Distance car travels, Dc = 180 mi.

Rate of car = Rc

Rate of truck, Rt = Rc - 20

Time, T, is the same for both, so

T = D / R, therefore,

Dt / Rt = Dc / Rc

120 / (Rc - 20) = 180 / Rc

120Rc = 180(Rc - 20)

120Rc = 180Rc - 3600

120Rc - 180Rc = - 3600

- 60Rc = - 3600

Rc = - 3600 / - 60

Rc = 60

Rt = 60 - 20

Rt = 40

The truck is travelling an average of 40 mph and the car is travelling an average of 60 mph.

Distance truck travels, Dt = 120 mi.

Distance car travels, Dc = 180 mi.

Rate of car = Rc

Rate of truck, Rt = Rc - 20

Time, T, is the same for both, so

T = D / R, therefore,

Dt / Rt = Dc / Rc

120 / (Rc - 20) = 180 / Rc

120Rc = 180(Rc - 20)

120Rc = 180Rc - 3600

120Rc - 180Rc = - 3600

- 60Rc = - 3600

Rc = - 3600 / - 60

Rc = 60

Rt = 60 - 20

Rt = 40

The truck is travelling an average of 40 mph and the car is travelling an average of 60 mph.