a triangle is always 180, in other words you will add all the corners equal to 180
ex (for first question) - 7x -2 + 4x + 5x - 10 = 180
you add like terms, the x with x and single numbers with numbers, which results in 16x - 12 = 180. then you do the original operation "what you do to one sign of the equal side you do to the other"
