A college student invested part of a $25,000 inheritance at 7% interest and the rest at 6%.  If his annual interest is $1,670 how much did he invest at 6%?  If I told you the answer is $8,000, in your own words, using complete sentences, explain how you would solve the problem.

Solve each equation by factoring.

x² + 8x + 15 = 0

Complete the square to make each binomial a perfect square triangle.

x² - 12x

Use the quadratic formula to solve each equation.

6x² + x - 2= 0

3x² + 18x + 15= 0

Solve each problem.