Subtract (x+109) from 180; the result is 71-x. The reason for doing this is that we want to equate "corresponding angles." 71-x and x+89 are corresponding angles. Set them = to one another and then solve the resulting equation for x:
71-x = x+89 -18 = 2x, so x = -9
Now let's determine the angle x+89. Since x=-9, that angle is 80 (degrees).
So those to angles added together equals 180° thus all you have to add those together and set it equal to 180 to find hat x equals, and then add 89 to it to find the highlighted angle.
x+109+x+89=180
add the numbers and x's together
2x+198=180
subtract 198 from each side
2x = -18
divide each side by 2
x = -9
Put -9 in for x in the equation x+89 to find that angle
