Algebra 1
Hey so I got this question wrong on my quiz and I'm doing corrections, so I was wondering if anyone is willing to help me figure out this problem (don't know what I did wrong!) And please explain it! If you don't know the answer, or you're not sure, DON'T ANSWER! Thank you so much and any links will be reported!!

Problem:

-3√18 + 5√72 - √2