Answer:
45
Step-by-step explanation:
Let the three quantities be x, y and z.
[tex] \because \: average = \frac{sum \: of \: quantities}{no \: of \: quantities} \\ \\ \therefore \: 15 = \frac{x + y + z}{3} \\ \\ 15 \times 3 = x + y + z \\ \\ \huge \purple{ 45 = x + y + z}[/tex]
