Think about the problem this way.
The heat lost by the silver when it is put into the water must equal the heat gained by the water. We must solve for the final temperature, T, of the water. You must know the specific heat of both the water and silver to solve. Get the data from a table. Specific heat of AG is .24 and water is 4.18
Heat lost by the silver is (20)(.24)(350 - T)
Heat gained by the water is (200)(4.16)(T-30)
Set the two expressions equal to each other and solve for T.