Complement and Supplement of an angle

Find the measure of angle A if 5 times the complement of angle A is 150 greater than the supplement of angle A.

I have this

Let s be supplement and c be complement.

180-A = s

90-A= c

5c-150= s

I plugged the above in.

5c-150=180-A

Then plugged in my definition for c.

5(90-A) - 150 = 180 - A

450-5A + A=180 + 150

-4A=330-450

-4A=-120

A= 30.

Huh. That's strange I got it right this time.

ANyway, there must be an easier way to do this. I think I used some things the book hadn't taught yet.

Thanks!