exam Maths Puzzle Numerical Ability

IS this a function?
{(3,7),(3,8),(3,-2),(3,4),(3,1)}

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exam Other Question
Can you help me solve this equation?

P = 2L + 2w

w = Bob owns a watch repair shop. He has found that the cost of operating his shop is given by c(x)=4x^2-304x+71, where x is the number of watches repaired. How many watches must her repair to have the lowest cost?

Thanks.