The number of caps a new online store sells increases by a factor of 4 each month. the function f(x) = 4^x represents the number of caps sold in month x. when does the store sell 64 caps? a. month 4 b. month 3 c. month 2 d. month 16

Solve 64 = 4^x.  Take the log of both sides of this equation, obtaining:
                                              log 64
log 64 = x*log 4.  Then x = = 3                 (Month 3)
                                               log 4