Final answer:
The company should expect to sell 99 pairs of sandals if the outside temperature is 90 degrees.
Step-by-step explanation:
To find how many pairs of sandals should the company expect to sell if the outside temperature is 90 degrees, substitute x = 90 into the linear model y = 0.6x + 45.
Substituting the value, we have: y = 0.6(90) + 45 = 54 + 45 = 99.
Therefore, the company should expect to sell 99 pairs of sandals if the outside temperature is 90 degrees. The answer is option a) 99.