The problem is missing some parts:
First, how many parts should you purchase each time you place an order.
H=.2*$4 = $0.80
S= $800
R = 50,000
Q = 2SRH
= 2(800) (50000) (.8)
= 10,000 units
The second question is how many timer per year will you place orders.
Required order = R/Q
= 50000/10000
= 5 times