I need to simplify these boolean expressions.

1. The problem statement, all variables and given/known data

Problem A:

a`b`d+a`bd`+bc`d`+bcd`+ab`c`d+b`cd

Problem B:

a`b`cd+a`bd+abcd+a`b`d+acd+abd+ab`c`d

Problem C:

a`b`c`d`+a`b`cd`+a`bd+ab`c`d`+bd+ab`d`

2. Relevant equations

abc means a AND b AND c

a+b means a OR b

a` means NOT a

I have been working on these for over 6 hours and I still have a mess. I look at the rules and try to apply them, but I know my answers are incorrect.