Since an equilateral triangle has three equal sides you need to divide the perimeter by 3 to get 3 equal lengths.
First - set it up as division and get:
(3x+30)/3
Second - to divide by three you need to factor out 3x+30 and you will get:
3(x+10)/3
Third - you have to divide the two 3'sand get:
1(x+10)/1 = x+10
ANSWER:
X+10
And if you wanted to check you could add x+10+x+10+x+10
Combine like terms and you'll get back to the perimeter of 3x+30