Answer:
The answer is below
Explanation:
a) A linear function shows the relationship between variables. A linear equation is in the form: y = mx + b, where m is the rate of change, b is the value of y when x = 0, y is the dependent variable and x is an independent variable.
Let U represent the number of umbrellas and p the price of the umbrella. At $10 the number of umbrella sold is 18000, it can be represented as (10, 18000) i.e. (p, U)
At $16 the number of umbrella sold is 9000, it can be represented as (16, 9000).
The linear function is determined using:

Given (10, 18000) and (16, 9000):

b) At p = $20, The number of umbrella is:
U(20) = -1500(20)+33000
U(20) = 3000 umbrella