For each of the following situations, write down the formula and determine if it defines a linear function: b) The area of a square with side a is S. What is the formula for the dependence of S on a?
c) The length of a rectangle is 10 cm, while the width is x cm. The area of the rectangle is A. What is the formula for the dependence of A on x?
d) A pedestrian left his house and started walking on a straight street at the speed of 5 km/h. In t hours he walked S kilometers. What is the formula for the dependence of S on t (t≤5)?