(2)0. 12,36 ; 10,90 ;

(3) When the knob is turned to 36, it saves the most fuel, and when the knob is turned to 90, it saves the most time. It is impossible to save time and gas at the same time.

Note: Question (3) can only be clearly expressed, and the way and words are not necessarily expressed in this way.

Note: the most fuel-efficient knob is located near 36, close to the golden section point of 0 ~ 90 (36 90 = 0.4).