30 tens - 3 tens 3 tenths

We are given the expression 30 tens - 3 tens 3 tenths. In this case, a number proceeded by "tens" means that the number is multiplied by 10 while "tenths" means that the number is divided by 10. In this case, 30*10 - 3*10*3/10 equal to 300 - 9 or 291. 

6 book set = 69.95
6 separate books = 14.95 = 6x14.95= 89.70
69.95<89.70, 6 book set is a better deal