Understanding a formula

The formula says find the value in row 12 that matches the value in cell P2 using MATCH(P2, $F$12:$N$12,0), and return cells from that column, rows 13 to 150 using INDEX($F$13:$N$150, ,MATCH(P2, $F$12:$N$12,0)) and sum the values from that range whenever the value in column C matches P2. Then divide by 15, round it to zero decimal places, and multiply by 11.35.

Your error is the mismatch in the number of cells between the ranges passed to SUMIFS: they must be the same size. Your are using a column from row 13 to row 150, and trying to match it to values in column C, rows 14 to 150. So this one change should work:

=ROUND(SUMIFS(INDEX($F$13:$N$150, ,MATCH(P2, $F$12:$N$12,0)), $C$13:$C$150, P2)/15,0)*11.35

Break the formula down into its components to better understand it.

INDEX($F$13:$N$150, ,MATCH(P2, $F$12:$N$12,0))

INDEX/MATCH are often used in conjunction. They act quite similarly to V/HLOOKUP, but with a few differences. In this instance, the cell range $F$13:$N$150 is being "indexed". This means that the ordinal range returned by the MATCH() function will be used as a data criteria range for the SUMIFS. Since the $F$12:$N$12 range in the MATCH() portion is being referenced, the match of P2 within the row range of F12:N12 will be used as the column index value for INDEX().

SUMIFS(Data_Range_from_INDEX/MATCH, $C$14:$C$150, P2) is summing all the data within the data range from INDEX/MATCH whose ordinal coordinates match that of the range $C$14:$C$150 that fits the criteria specified in P2. However, you could have used a regular SUMIF vs. SUMIFS for this, since there is only one criteria.

The rest is straightforward. The value that SUMIFS() produces is then divided by 15, and rounded to 0 digits. This entire number is then multiplied by 11.35.

It would be easier to explain further if the data which these values were being pulled from were provided.

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