book Maths Puzzle Numerical Ability

What is the vertex of this parabola? (x-4)^2=2y

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book Other Question

A collection of dimes and quarters is worth $5.45. There are 32 coins in all. How many of each type of coin are there?

so for this one, i know that we should make D=dimes and Q=quarters.. but thats where my knowledge ends. How do you solve this by graphing?

3y=3x-6
9=8x-9y