Planks cost $3 each and plywood sheets cost $5 each. nick purchased 9 planks and 2 sheets of plywood. how much money did nick spend all together? explain how you solved the problem.

So if nick purchased 9 planks and they cost 3$ each then you could add 3 nine times or multiply 3x9 which is 27$
now the same with the plywood but i would be 10$ he spent on those
now add 27 to 10 and you get 37$ 
so he spent 37$ all together

The first one, i believe, would be correct. all the others have one thing in common, and that's that they have repeating numbers. in the second one, x and y have repeating 6's and 3's, and in the third, x and y have repeating 6's as well. in the last one, there are repeating 3's. the first one has no repeating numbers.