Are You Smarter Than A 3rd Graders Homework?

Gameboys 3rd grade math homework is right up there with quantum physics and I'm not even joking. He usually gets a power hour at his after school care, where the young smart college kids babysit counsel the kids and help with home work. They couldn't even help him. Great!
I take one look at it and it's all about grouping numbers in a Sudoku type way so that the rows and columns add up to a certain total only using the series of numbers like 1-9. My brain has never wrapped itself around Sudoku much less have it have to actually total an amount and be in a certain order as to not repeat numbers. AAAKKK!
I figure my highly intelligent husband, who can figure quantum mathematics in his head could easily do this. He lives for this kind of stuff. He messed around with it and he's having trouble. Of course it took everything I had to wipe the smug look off my face. I'm back to the drawing board.
Is this really homework for an 8 year old or to have quality family time together while mom and dad try to wrap their brains around this stuff?
If anyone out there in blog land could give us some kind of equation to solve this I'd be ever grateful!!!

--Put the numbers 1-9 in the square so that every horizontal and vertical row and the diagonal add up to 15. In other words it's a three block square with nine squares. No repeating numbers of course!
***Updated!** Houston we have a winner! Ya'll must have sent me some good bloggy vibes cause some how I figured it out, not less than 5 minutes after I posted this. I've been working on it since we got home. High fives all around and hubs had to put the boys to bed. Can I get a "you go girl!" On to the last question....
I won't even tell you the last question which deals with 13 numbers and three in a row adding up to 21.

Please tell me it's gonna get easier. If you give me a formula and what I need to solve, I can do it for the most part... This is beyond me!