Please help me combine these two equations to find what m and b are.

Julie was able to walk 16 km through the zoo in 6 hours. how long will it take her to walk 24 km through the zoo?

If f(x) = 3x2 - 2x+4 and g(x) = 5x + 6x - 8, find (f-g)(x).

The half-life of a certain material is 0.004 second. approximately how much of a 20-gram sample will be left after 0.016 second? a. 5 grams b. 16 grams c. 0.32 gram d. 1.25 grams