3 problems on review of algebra 2

Hi, I really need some help on these 3 problems of my algebra 2 review.

They are:

1. Wendy, a loan officer at a bank, has $1,000,000 to lend and is required to obtain an average return of 18% per year, If she can lend at the rate of 19% or at the rate of 16%, how much can she lend at the 16% rate and still meet her requirement?

2. How many cubic centimeters of pure hydrochloric acid should be added to 20cc of a 30% solution of hydrochloric acid to obtain a 50% solution?

3. The line x-2y=-4 is tangent to a circle at (0,2). The line y=2x-7 is tangent to the same circle at (3,-1). Find the center of the circle.

Thanks for your help.