Puzzle 1
The concentration of a certain chemical in the bloodstream t hours after injection into muscle tissue is given by

C = 3t( 27 + t³) ^-1,

where 0 ≤ t. When is the concentration greatest?

Puzzle 2
The number of kilometers M per liter for an experimental automobil engine is given by

M = 3200x(1600 + x²) ^-1, 16 ≤ x ≤ 100,

where x is the speed of the automobil in kilometers per hour.
Determined the speed in the specified interval that yields the greates fuel economy.