Suppose that there are only 2 firms in the entire market. Their supply curves are given as follows:

S1(p) = 0, if p< 10 and

S1(p) = p-10 , if p>= 10

S2(p) = 0 , if p=15

S2(p) = (p-15), if P>15

Market supply for price , p = 15 will be ______.

Sm(p) = 5

The correct answer is Option 4: Sm(p) = 5

At price equal to 15, only the first firm will supply the product because the supply of other firm is 0 at this price (15) as mentioned in the question itself.

Thus, at P =15, 

        Sm(p) = Supply of Firm 1 + Supply of Firm 2

                  = (p-10) + 0

                  = 15- 10 + 0

                  = 5