It takes X minutes for Class A to plant trees alone, and x+50 minutes for Class B to plant trees alone.

Class A and Class B plant trees together 1 hour.

So 60/x+60/(x+50)= 1.

60(x+50)+60x=x(x+50)

120x+3000=x？ +50 times

x？ -70x-3000=0

(x-35)？ =35? +3000=4225=65?

x=35 65

X=35+65= 100 because of x>0.

x+50= 150

It takes 100 minutes for Class A to plant trees alone, and 150 minutes for Class B to plant trees alone.