We have
Diameter of the rear wheel D =1.5 m
Distance covered in one revolution = circumference of the wheel = πD=1.5πm
Now, Distance covered in 80 revolution =80×1.5π=120πm
Let d be the diameter of the front wheel.
Now, Distance covered in one revolution by front wheel =πd m
Now, Distance covered in 240 revolution by front wheel =240πd m
Distance covered by front wheel in 240 revolution = Distance covered by rear wheel in 80 revolution
=>240πd=120π
=>d=12 m
=>d=0.5 m