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2.30+0.4-0.88+1.33 can u explain the answer to this why the answer is 3.15

Asalesperson earns $320 per week plus 8% of her weekly sales. the expression representing her earnings is 320 + 0.08x. which of the following describes the sales necessary for the salesperson to earn at least $1000 in the one week?

If cos(2x) = tan^2(y), show that cos(2y) = tan^2(x).