Tap A fills up a water tank in 45 mins.

Tap A fills up_____(ugh soo right here for the answer... do i put it in a fraction or something?)of the tank in one min.
Tap B fills up the same tank in 75 mins.
Tap B fills up_____of the tank in one min
Tap A and tap B fill together up(do i add right here?)____of the tank in 1 minute.
tap A and tap B together fill up the tank in _____mins

Yes. You need a fraction for Tap A. In one minute it will fill 1/45 of the tank.

Please tell us what you think the other answers are, and we'll be glad to critique your answer.

do i add 1/45 and 1/75?

Yes. That tells you what fraction of the tank that both taps will fill in one minute.

What is your answer to the last question? How long will it take both taps to fill the tank?

28.125

To get the answer for the last question, you need to add the rates at which Tap A and Tap B fill the tank in one minute, which are 1/45 and 1/75 respectively. Adding these fractions will give you the combined rate at which both taps fill the tank in one minute.