book Maths Puzzle Numerical Ability

Use FOIL to multiply:
(5x - 8)(x - 7)

ANY HELP :)

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book Other Question

Could you explain this to me?:

How many liters of paint are needed to paint the walls of a rectangular prism-shaped room that is 6m x 4m x 2.5m if 1 L of paint covers 20 m2? (assume there are no doors or windows)

Thanks! I'm not understanding "no solutions" or infinitely many solutions where appropriate...How do I tell the difference?
y = x
y = 3x + 2