how many positive integers less than 1000
a) are divisible by 7 but not by 11?
b) are divisible by either 7 or 11?
c) are divisible by exactly one of 7 or 11?
d) are divisible by neither 7 nor 11?
e) have distinct digits?
f) have distinct digits and are even?
Please help me explain step by step. I am very lost in counting.