Plz answer and i'm stuck

each of two congruent sides of an isosceles triangle is 2n + 7 and the third side is 3n. write two equivalent expressions for the perimeter, also combine like terms to find the perimeter

part two
a student wrote 2(2n+7)+2(3n) or 3(2n+7+3n) why is this wrong?

The equations could be
(2n+7)+(2n+7)+3n
or 2(2n+7)+3n
When we combined like terms it could be
4n+14+3n

2(2n+7)+2(3n) is incorrect because in a triangle there are 3 sides, the measure of two of the sides are 2(2n+7) and the third side is 3n however, he/she put "2(3n)" which would show there are 2 sides with the measure 3n