$($Relativity $-$ Velocity Addition$)$ A rocket ship is passing by earth at $90\%$ the speed of light. It then fires a missile at $80\%$ the speed of light straight forward from the ship. For an observer on earth, how fast is the missile going?

a$)1\mathrm{.}70$ c

b$)2\mathrm{.}36$ c

c$)0\mathrm{.}98$ c

d$)0\mathrm{.}42$ c

e$)$ None of the above.