The air pressure inside jason's bike tires decreases by about 6% each week. the original pressure was 45 pounds per square inch (psi). what is the tire pressure after 6 weeks?

Lets do this week by week 
beginning pressure 45 pounds 
end of week 1 
45 *.06 = 2.7
45 - 2.7 = 42.3
end of week 2 
42.3 * .06 = 2.538
42.3 - 2.538 = 39.762
end of week 3 
39.762 *.06 = 2.38
39.762 -  2.38 = 37.37
end of week 4
37.37* .06 = 2.2425
37.37628 - 2.2425= 35.12
end of week 5
35.12 * .06 = 2.107
35.12 - 2.107 = 33.012
end of week 6 
33.012* .06 = 1.98
33.012 - 1.98 =31.03

Here is the fast way to get to this answer. 
do 1-.06 = .94

then do 
45(.94)(.94)(.94)(.94)(.94)(.94)  = 31.04