Question

In ΔABC, what is the value of x?

5.5
6.5
55
65

Answer 1

The 3 angles of a triangle add up to 180 degrees so:-

10x - 10 + 10x + 8 + 8x = 180
28x = 180 + 10 - 8
28x =  182
x =  6.5 (answer)

Answer 2

The internal angles of a triangle adds up to 180.
10x-10+8x+10x+8=180
Collect like terms
10x+8x+10x=180+10-8
28x=182
Divide by 28 throughout
28x/28=182/28
X=6.5