Who's JD? I'll guess that's money in some country.
This one requires a bit of analysis before writing the equation. 3pm is the time the price changes so
11am to 5 is 4 hours before, 2 hours after, JD18
9am to 7 is 6 hours before, 4 hours after, JD31
OK, let's call the morning rate x and the evening rate y.
a.
Rate times hours is cost; we have to add up the morning and evening:
4x + 2y = 18
6x + 4y = 31
b.
We multiply the first equation by 2,
8x + 4y = 36
Subtract the second equation,
2x = 36 - 31 = 5
x = 5/2
2y = 18 - 4x
y = 9 - 2x = 9 - 5 = 4
Answer: Our solution is the price was JD 2.50 before 3pm and JD 4 after.
Check:
2.5(4) + 4(2) = 18 good
2.5(6) + 4(3) = 31 good
