Answer:
x = 5
Explanation:
first of all, the two given angles are alternate angles, meaning they are of the same value in terms of degrees so that means we can write it as 21x - 5 = 100 and then we can work out x from here. we can ads 5 to the left to get rid of -5 but then we would also have to add 5 to the right. we are left with 21x = 105 so now we have to divide both sides by 21 to get x = 5 because 105 ÷ 21 = 5 and 21x ÷ 21 = x