Greetings!
To convert a mixed number into an improper fraction, you multiply the whole number by the denominator. Then, you add that number to the numerator.
Examples:
a)
8 1/4
8*4=32
32+1=33
=33/4
b)
3 4/5
3*5=15
15+4=19
=19/5
I'll let you attempt the last one on your own. :)
Hope this helps.
-Benjamin