Ew i hate these⇆∈√,×≈↓⇒∈∧⊂∴∵√²³Ф≠→Ф
You have to find out what 15% of $78 dollars is. If you have to do this in your head and not on a calculator you can find 10%, then cut that number in 1/2 and add it to the answer. So 10% of $78 is 7.8 so $7.80. You can divide 7.80 by 2 and get 3.9 and add that to 7.8 which is 11.70. So 15% of $78 is $11.70.
Answer is 10 and 170, complementary angles are 90°, while supplementary angles are 180 in total, if angle A is 80 then you subtract 90 by 80 and you get 10, so that is angle B, So then you are asked what is angle C. Which is part of the supplementary angle so you take the 10° that you got from B and then you subtract 180 by the 10, And thats how you get 170 and that's how you know that C is 170 (hope this explanation helps)
