Solution: it takes x weeks to complete a single task, and it costs one million yuan per week;

B it takes y weeks to complete it alone, and it costs b million yuan a week.

Judging from the meaning of the question:

1/x+ 1/y= 1/6

4/x+9/y= 1 (the specific step of solving the equation is omitted)

∴x= 10

y= 15

6a+6b=5.2

4a+9b=4.8

∴a=0.6

b=4/ 15

∴ A alone requires10 * 0.6 = 60,000.

B alone requires 15 * 4/ 15 = 40000.

Choose company B.