Acarpenter and can do a certain job in 18 days if the carpenter takes walks 1.5 times as fast as the 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