Question 191752
let  14  =  total  comm  spots

let  x  =  #  of  30  sec spots,  therefore  14-x =  #  of  60  sec spots

total  comm  time  is  11  min  =  11 *60  sec  =  660  sec

total  time   =  30  x  +  60 ( 14-x)  =  660

simplifying      30 x  -60  x  +  840  =  660

                         -30x  =  - 180

                               x=6    (  #  of  30  sec  spots)

                              and  (14-x)  =  14-6 = 8   (#  0f  60  sec  spots)

check    (6) (30)  + (8)  (60)  =  660  sec  =  11  min  ok