Apples cost £A per kilo and blackberries £B per kilo
3A+1.5B=9, 2A+4B=£13.20, so A+2B=£6.60 (dividing by 2)
Substituting for A:
3(6.60-2B)+1.5B=9
19.8-6B+1.5B=9
19.8-4.5B=9
4.5B=19.8-9=10.8, so B=10.8/4.5=1.2/0.5=2.4
Blackberries are £2.40 per kilo and apples are £6.60-2*£2.40=£6.60-£4.80=£1.80
A kilo of each cost £2.40+£1.80=£4.20