Equivalent expression for -3/7g+10

Choose the triangle with x equal to 17.

Four individuals pool money together to start a new business and agree to split the profits equally. n invests $6,000, x invests $2,000, y invests $8,000 and z invests $4,000. if the profits for the first month were $100,000, y receives than if the profits were divided in proportion to how much they invested.

What is the axis of symmetry of the function f(x)=-(x+ 9)(x-21)