Pineapple = 83p, coconut = 57p, melon = 62p.

If we assign the letters P, C and M to the fruits, and work in pence we have:

M + C = 119 (1)

M + P = 145 (2)

C + P = 140 (3)

Using (2) - (1) we have:

P - C = 26 (4)

And (3) + (4) gives:

2P = 166

P = 83

This can then be substituted back into (2) and (3). QED.