Given that 0 ≤ a < 2π, which of the following gives all solutions to the equation 2cos(2a) + 4cos a - 6 = 0
a. a= 0
b. a = π
c. a = 0 and π
d. a = 0 and 2π

You can ride your bike around your block 6 times and the whole neighborhood 5 times in 16 minutes. you can ride your bike around your block 3 times and the whole neighborhood 10 times in 23 minutes. how long does it take you to ride around the neighborhood?