Since there was five boxes of crayons and there was 3 crayons in each one, the would be 15 in total. (crayons) And there was three people, 15/3=5 crayons per person. Equation: 3x=15 x stands for the amount of crayons each person gets.
To find 10% you divide the amount by 10 so £1.80 dived by 10 is 0.18p. Therefore you want 10% OFF that amount so you do £1.80-0.80p and you are left with £1.00.