Help? Geometry class is tripping me out while trying to do make up work

If a 36 inch yardstick casts a 21 foot shadow, how tall is a building whose shadow is 168 feet? what is the scale factor

Mrs. blake's bill at a restaurant is $42.75. she wants to leave the waiter an 18% tip. how much will she pay in all, including the tip?

Which of the following values in the set below will make the equation 5x + 6 = 6 true? (only input the number.) {0, 1, 2, 3, 4}