Image Formation Questions

A boy is trying to start a fire by focusing Sunlight on a piece of paper using an equiconvex lens of focal length $10\text{cm}$. The diameter of the Sun is $1.39\times 10^9\text{m}$ and its mean distance from the earth is $1.5\times 10^{11}\text{m}$. What is the diameter of the Sun's image on the paper?