Your answer is:
V(n) = 30(0.95)^n
Why?
Well here is why!
Rate of decrease = 5%
Period, n = 10 days
Initial stock price = $30
Value of share price as a function of n:
Value, V(n)
Initial price = A
V(n) = Initial price(1 - rate)^n
V(n) = 30(1 - 0.05)^n
V(n) = 30(0.95)^n
Hope this helps if it did mark brainlist!