a carpenter and helper can do a certain job in 18 days if the carpenter takes walks 1.5 times as fast as the helper how long would it take each working alone?

Let
x-----------> time it takes the carpenter working alone
y-----------> time it takes the helper working alone

we know that
x+y=18 days------------>equation 1
x=y/1.5---------------> equation 2

I substitute 2 in 1
(y/1.5)+y=18----------> (y+1.5y)/1.5=18---------> 2.5y=18*1.5
2.5y=27-----------> y=27/2.5-----------> y=10.8 days

x+y=18--------> x=18-10.8---------> x=7.2 days

the answer is 
time it takes the carpenter working alone is 7.2 days
time it takes the helper working alone is 10.8 days