In terms of cards:
Ali=X
Belinda=2x
Charlie has 5 more cards than Belinda his will be 2x+5
a) Add up all of their number of cards which will be:
X+2X+2X+5
collect the like terms giving you 4x+5
in total they own 33 cards so the equation above will equal 33 making the equation 4x +5=33
b)Use the equation you got above to get the value of X alone so move the 5 over the equal sign making it negative so you have 4x=33-5
Making it 4x=28
Divide both sides by 4 so 4x dived by 4 leaving X alone then 28/4 giving you 7
So finally Ali has 7 cards.