$10(7+x)=75$ she charges $10 an hour = $10
$10(7+5x)=75$ she needs $75 + $5 tip = 5t 10*7=70 + 5 = 75
she needs to babysit 7hours in all..
she charges 10$ an hour , if she dose 7 hours she will have 70$ but there is an automatic tip of 5$ soo 70 + 5 = 75
dose this help?