Matching PO number with matchin negative value w/ corresponding positive value

I have a spreadsheet of invoices and credits. Is there a way to highlight both the positive and negatives values in column H if they have matching PO No in column C as well as matching positive and negative value in H? For example in row 5 and 6, there is a matching PO No in C as well as matching value in H, I would like Excel to highlight the values in H5 and H6.


Thanks.