使用For循环变量在Swift中选择一个数组项

I have a very simple question that I cannot find the answer to. I am trying to plug an array of x and y values through an equation, and fill an array with the answers. The error in this code is that the arrays don't accept numbers because "error: 'Range' is not convertible to 'Int'". How would I deal with this? This is done with Xcode 6.01 in swift playground. Thanks!I have a very simple question that I cannot fin