Ella earns $7.50 per hour baby-sitting, plus a $20 travel fee. Desiree earns $9.50 per hour walking dogs, plus a $12 supply fee. How many hours must the girls work to earn an equal amount of money? i need the equation and the solving steps : )

I’m pretty sure the equation is 7.50x+20=9.50x+12 then you subtract the x over and now it’ll be -2x+20=12 and then you do 12 - 20 and that is -8 and then -8 divided by -2 and that is 4. so maybe x equals 4? then plug it in and now you have to check your answer so you plug in the 4 and it is 7.50(4)+20=9.50(4)+12 and then that is 50=50. I MAY BE TOTALLY WRONG. but i tried to help at least