28.1-21.97 what is the answer and how do i get it

Find the greatest common factor of the followig monomials 21u^5v,3u^4v^6, and 3u^2v^5

Plz answer asap! i will reward brainliest and 12 points for these three questions!take notice: these three questions are completely different! 1) what is the percentage of sugar in the syrup made of 10 kg of water and 4 kg of suugar? 2) what was the original price if after 10% discount it became $450? 3) at first a price was decreased by 12%, then it was disounted again by an additional 5%. what is the percent of the total discount? , and remeber i will award brainliest and 12 points!

What is the expression equivalent to (3x^2-7)