Notice that we are given in algebraic form the measures of the three angles of a triangle. Recall that we know that the addition of all internal angles of a triangle must give 180 degrees
Then, we can write the following equation:
and now replace each angle measure by its algebraic form:
(2 x + 12 ) + (6 x + 20) + (6 x + 8) = 180
remove parenthesis and combine like terms:
2 x + 6 x + 6 x + 12 + 20 + 8 = 180
14 x + 40 = 180
subtract 40 from both sides
14 x = 180 - 40
14 x = 140
divive both sides by 14 to isolate x completely
x = 140 / 14
x = 10
We solved for the unknown.