Thank you for the opportunity to help you with your question!

sqrt(15+2x) = -x

take square of both sides

15+2x = x^2

x^2-2x - 15 = 0

x^2-5x+3x - 15 = 0

x(x-5)+3(x-5)=0

(x+3)(x-5)= 0

so the solution is (-3,5) option "D"

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