Please help

Hi please can anyone help in excel i have one cell set up to subtract another but it's not coming up with the right answer why? Here is what I have £14.55 in one cell and -£14.55 in another cell but the total keeps coming up with £29.10 but it should be £00.00 I'm fairly new with excel and only done a few basic courses please can any one help with what I'm doing wrong