Solution

153699

First name
Harvey Cardwell
School
Little Melton Primary School
Country
Age
9
Email address
office@littlemelton.norfolk.sch.uk

first I listed the weights of watermelon down below:
.the watermelon at the front weighs 7.35
.the watermelon on the left weighs 8.20
.the watermelon on the right weighs 6.45

because every gram equals 1 point I turned the kilograms into grams
7.35kg = 7350g
8.20kg = 8200g
6.45kg = 6450g

then I converted each weight into points:

7350g = 7350 points
8200g = 8200 points
6450g = 6450 points

the watermelon on the left get the most points(8200 points)

the watermelon on the left WINS!