The unit price per kg is $5, to find this divide the 9 kilograms into the price $45 the answer is what each kilogram is worth
10.00
-4.59
= 5.41
so 5.41 is your answer
Set x's equal
21x +35y = 7
21x + 12y = -39
Subtract from one another
23y = 46
Divide
y = 2
Hope this helps ;)