Here is the question of interest, along with the solution:
[ AMC Year 9 Intermediate Test Paper Question 3]
I fully understand the question and its requirements. But what I don't understand is the solution. On the sixth line of the solution, it says $108 + 2x = 180$. I do not understand how this is equal to $180$. It's probably a simple case of angle mathematics but I am struggling to figure it out.
A reason why $108 + 2x$ is equal to $180$ in this case would be sufficient.
Thank you,
The sum of the internal angles in any triangle is $180^\circ$.
There is more information in this Wikipedia article.