Having Characters Appear After Entering Values?

I work in a fruit and veg business and they are using parchment and quill still, well it certainly feels that way. I have been asked by customers to provide an online order form which i will email to them and they can fill in and email back, i scanned an invoice and used OCR to upload it to excel and it has come out quite well.

Basically there are three columns of product lines and then directly to the right of each product is a column i have entitled Box & KG respectively, if the customer types a number into the box column i want it to automatically add 'Bx' to the end so this if they typed 5 in a cell in the box column it would look like this '5 Bx' (obviously without the quotes), and the same for the KG column but it would denote 5 KG instead, also i would want it to add in the space as well after the value.