Answer:
Jumper costs £13
Step-by-step explanation: (s = shirt j = jumper)
We know that 2s + 1j = £29
We also know that 1s + 1j = £21
29-21 = £8
This means that the shirts cost £8 each
We now need to multiply: 8 x 2 = £16 which means that the shirts in total cost £16
So, 29 - 16 = £13 which means one jumper costs £13