In Pennsylvania, the state income tax is directly proportional to gross income. Suppose you were working in Pennsylvania and your state income tax deduction was $43.50 for a gross monthly income of $1500. Which of the following mathematical models gives the Pennsylvania state income tax, y, in terms of gross income x?

a. y = 0.029x

b. y = 34.48x

c. y = x/0.029

d. y = -34.48x

e. None of the others