Let us suppose cost of 1 watermelon be x.
Cost of 6 watermelons = 6x.
It is given after buying 6 watermelons, he had $25.50 left.Total amount William spends on vegetable is $45.
We can form an equation with above information's
6x+25.50=45
To solve for x we isolate the x term .25.50 is added to the x term .
Opposite of addition is subtraction .Subtracting 25.50 both sides we have:
6x=45-25.50
6x=19.50
Dividing both sides by 6
x=3.25.
Cost of each watermelon is $3.25.
