Some adults and children went to a movie. 12 people total went.
An adult ticket costs $8 and a child ticket costs $5.
They spent $72 total.
How many adults went and how many children?

Then the best way to phrase it would be to jump right into the question without I need your help, because saying so makes it sound as though you have more of an urgent, sensitive, personal problem than a simple question or two (they might be a bit taken aback by the phrase).

However, if you have several questions (let's say more than 2), or if you just want to sound a bit more polite, you could preface the content with a phrase like I was wondering I you might be able to answer a few questions of mine, or, I have a few questions that I was hoping you might be able to help me with.