Answer:
60
Explanation:
The perimeter of the triangle is found by adding up the 3 sides
5+5+ unknown side = 15
10+unknown side = 15
Subtract 10 from each side
10-10 +unknown side = 15-10
unknown side = 5
All 3 sides are length 5
Since all 3 sides are the same, it is an equilateral triangle.
If it is an equilateral triangle, all 3 angles will be the same.
There are 3 angles and they add up to 180
x+x+x = 180
3x = 180
Divide by 3
3x/3 =180/3
x = 60