a) To calculate the cost of t-shirts, we need to consider the flat design rate and the cost per t-shirt. The formula to calculate the cost is as follows:
Cost = (Flat Design Rate) + (Number of T-shirts * Cost per T-shirt)
In this case, the flat design rate is $15, and the cost per t-shirt is $7.50. Let's write the function C(t) where t represents the number of t-shirts:
C(t) = 15 + (7.50 * t)
b) To calculate the income generated from the sale of t-shirts, we need to multiply the selling price per t-shirt by the number of t-shirts. The formula is as follows:
Income = Selling Price per T-shirt * Number of T-shirts
Here, Teemu has decided to charge $10 per t-shirt. Let's write the function I(t) where t represents the number of t-shirts:
I(t) = 10 * t