if there are 9 small boxes that contains 10 pens in each box that is a total of 90 pens. 2 large boxes which has 15 pens in each box that is a total of 30 pens. so all together you have 120 prizes. you need 200 so you subtract 120 from 200 which leaves you needing 80 prizes. your answer is 80 more prizes.
A 25% discount means u paid 75%
75% of the original price is 18...
0.75x = 18.....with x being the original price
x = 18 / 0.75
x = 24 <== the original price
I have no clue let me do the work and I’ll comment it under here
Part (a)

By similar logic, the answers to the other parts are
(b) 1.75
(c) -2.19
(d) 0