Find the Particular Solution of the Differential Equation $\frac{d y}{d x}+y=2 e^{x} ; y=21$

Multiple Choice

Find the particular solution of the differential equation.
- $\frac{d y}{d x}+y=2 e^{x} ; y=21$ when $x=0$

A) $y=e^{x}+20 e^{-x}$
B) $y=4 e^{2}+20 e^{-x}$
C) $y=21 e^{x}$
D) $y=2 e^{x}+18 e^{-x}$