Qd = 900 - 10p

p = 15 + 0.05Qs

making Qs the subject of formular

p - 15 = 0.05Qs

Qs= (p-15)/0.05

then now to solve the equlibrium

Qd=Qs

900 - 10p = (p-15)/0.05

(900 - 10p)* 0.05 = p - 15

45 - 0.5p = p - 15

45 + 15 = p + 0.05p

60 = 1.05p

p = 60/1.05 = 57.1

insert p into Qd

Qd = 900 - 10(57.1)

   = 900 - 571

 Qd  = 329