Answer: No, 40 months isn’t reasonable.
Explanation:
For Shellie: 40*3 = 120 cm in 40 months
For Carley: 40*2 = 80cm in 40 months
Next we add the amount of hair they have already to the amount of centimeters would grow.
Shellie: 120+10 = 130cm
Carley: 80+20 = 100cm
So if the girls wanted to cut their hair at the exact length, 40 months isn’t a reasonable solution.