For the given x and y variables, decide whether y is or is not proportional to x. (a) y is the cost of x gallons of gasoline. (b) y is the perimeter of a square whose sides have length x. (c) y is the area of a square whose sides have length x. (d) y is the sales tax in Idaho of an item that costs x dollars. (e) y is the taxi fare for a ride of x miles. (a) y is the cost of x gallons of gasoline. y proportional to x.