800 at 4.25% simple interst for 6 years

Which of the following contains a variable?

If f(x)=x+7 and g(x)=1/x what is (fog)(x)

Acentral angle measuring 160 degrees intercepts an arc in a circle whose radius is 4. what is the length of the arc the circle formed by this central angle? round the length of the arc to the nearest hundredth of a unit. a) 4.19 units b) 6.28 units c) 12.57 units d) 12.57 square units