A car park charges a certain rate per hour before 3 pm, and a higher rate per hour
after 3 pm. Parking from 11 am to 5 pm costs JD 18, and parking from 9am to 7 pm costs JD31. Find the rates charged before and after 3 pm.

The rate charged before 3pm is JD 2.5 and the rate charged after 3pm is JD 4.

Let

The rate charged per hour before 3 pm be x.

The rate charged per hour after 3 pm be y.

From 11 am to 5 pm cost JD 18 and it is 6 hours . 4 hours before 3 pm and 2 hours after 3pm

Therefore,

4x + 2y = 18

From 9 am to 7 pm cost JD 31 and it is 10 hours . 6 hours before 3 pm and 4 hours after 3pm.

Therefore,

6x + 4y = 31

let's combine the equation.

4x + 2y = 18

6x + 4y = 31

8x + 4y = 36

8x - 6x = 36 - 31

2x = 5

x = 5 / 2

x = 2.5

6(2.5) + 4y = 31

15 + 4y = 31

4y = 31 - 15

y = 16 / 4

y = 4

Therefore, the rate charged before 3pm is JD 2.5 and the rate charged after 3pm is JD 4.

learn more on simultaneous equation here; link

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

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

the answer is two. hope this !