ช่วยอธิบายวิธีทำหน่อยค่ะ

1) The mass m (in Mg) of the fuel supply in the first-stage booster of rocket is m = 135 - 6t - t ยกกำลังสอง where t is the time ( in seconds) after lunch. When does the booster run out of fuel?

2) Pastry chef Lauren and her assistant chef Mike are preparing fancy desserts for banquet. The job would take Mike, working alone, 9 hours longer than it would take Lauren, working alone. Working together, Lauren and Mike can complete the job in 20 hours. How long would it take each chef to do the job, working alone.

3) Medical studies of stroke use Poiseuille's law, which says that the resistance (R) to flow of a blood vessel is directly proportional to length ( l ) and inversely proportional to the fourth power of the radius ( r ).
(a). Write an equation representing this statement of variation.
(B). If R = 25 when l = 12 and r = 0.2, find R as r increases to 0.3 while ( l ) is unchanged. Round answer to the nearest tenth.