Answer:
x = 4
Step-by-step explanation:
that's an equilateral triangle, 3 equal side and 3 equal angles of 60°,
so 10x + 20 = 60
solve with an equation
10x + 20 = 60
10x = 60 - 20
10x = 40
x = 40 : 10
x = 4
--------------------------
check
10 * 4 + 20 =
60°
the answer is good
