excel - How do we change column value and keep row constant in spreadsheet formula?

Question

I have to calculate the value of cells A1 till A10 and it takes values from M21, N21, O21, and so on till V21.

How can I write a formula to calculate the same?.

I tried =M$21 to keep row 21 constant, but while dragging the formula down from A1 till A10, it doesn't change the column ref as it's dragging down.

How can I change the column reference to change while dragging the formula down from A1 till A10?.

Answer 1

I would index across the columns based on the current row:

=INDEX($M$21:$V$21,ROW())