Somebody please help me :(

What is the effect on the graph of the parent function f(x) = x when f(x) is replaced with 3f(x)? a) shifts the line 3 units up b) shifts the line 3 units down c) increases the slope of the line by a factor of 3 d) decreases the slope of the line by a factor of 3

8litres of paint can cover 129.6 m². how much paint is required to paint an area of 243m²?

P= price tax is 4% added to the price. which expression shows the total price including tax?