1. Write a Python script that prints the total number of A's in sequences
given in FASTA format in a file called dna.fasta. The input may contain 
more than two sequences of any length. 

For example if the file contains 

>human
ACCGT
>mouse
GTGATAAA
>cat
GTGA

then the output of the program should be 

6

Your program should work for any sequences and not just the ones in the 
example.

2. Write a Python program that prints length of the longest
sequence in the file dna.txt given in FASTA format. 

For example if the file contains 

>human
ACCGT
>mouse
AGTTATATA
>cat
AGT
>dog
GTGTATA

then the output should be 

9

Your program should work for any number of sequences and not just the 
given example.

3. Write a Python script that takes from the user an input DNA 
sequence and prints the percentage of A's, C's, G's, and T's. 

For example if the user types

AGGTGACCCT

then the output should be

A: 20
C: 30
G: 30
T: 20