Try this solution:
dx/siny=dy/cos2x;
sinydy=cos2xdx;
cosy=-1/2 sin2x+C.
(16 - 4) ÷ 2
This would give you $6, so that is how much they expect you to spend per meal.
From the trigonometry:
tan θ = (sin θ) / (cos θ)
cot θ = (cos θ) / (sin θ)
∴ tan θ + cot θ = (sin θ) / (cos θ) + (cos θ) / (sin θ)
= [ sin² θ + cos² θ]/( sin θ cos θ) = 1 /( sin θ cos θ )
note : sin² θ + cos² θ = 1