18/x+8/(x-12) =/kloc-0 /→ x = 4 or x=24, excluding x = 4, so x=24.

A It takes 24 days to do it alone.

2.( 1) Set the ship x: 8x-5 (9-x) = 7; X=4。 So there are four big boats and five small boats.

(2)8*4+5*5=32+25=57 people

3. (360+160)/(0.9-0.8) = 5200 yuan