Excel, how to find column number of min value

To get the column number, use

=MATCH(1, (1:1="qtr02")*(2:2=2012), 0)

This is an “array formula”, so, after you type it, you must press Ctrl+Shift+Enter.

• 1:1 refers to all of row 1.  If you’d prefer, you can use A1:I1 to refer to just the cells that have data.
• (1:1="qtr02") looks for qtr02 in row 1 (or the designated cells, as appropriate) and constructs a Boolean array of the results.  In this case, the array is {FALSE, TRUE, FALSE, FALSE, FALSE, TRUE, FALSE, FALSE, FALSE} because the second and sixth columns contain qtr02.
• Likewise, (2:2=2012) creates an array of where the 2012s are in row 2: namely, {FALSE, FALSE, FALSE, FALSE, TRUE, TRUE, TRUE, TRUE, FALSE}.
• *, of course, is multiplication.  Since this is an arithmetic operator, it converts its operands to numbers: FALSE → 0 and TRUE → 1.  It then multiplies the two arrays pairwise.  This results in a 1 in each position where each of the operand arrays has a 1 (TRUE) and 0 elsewhere — in other words, the columns where both conditions are true.  This is equivalent to a logical AND function.  Excel has a function called AND() that does the exact same thing, but, unfortunately, it doesn’t work on arrays.  Using * is a kludgy trick to get around this limitation in the AND() function.
• And then, of course, MATCH(1, array, 0) finds the first element in the array that contains a 1.

=A1*$L$15

The dollar sign specifies an absolute (fixed) reference. Without the dollar sign, you'll get a relative reference by default, which is what you're seeing when you autofill.

More info here.