Question 946818
I assume you mean "at a rate of 3000 ft per minute".
When time is equal to zero, altitude is 40000. 
a){{{A=40000-3000t}}}
b){{{A(6)=40000-3000(6)}}}
{{{A(6)=40000-18000}}}
{{{A(6)=22000}}}
22000 feet