How to increase price by 20% when value entered in SQL is VARCHAR

I am trying to increase the price of all items that are monitors by 20% but the current line is VARCHAR so when I try to increase by 20% I get the following error:

Msg 8114, Level 16, State 5, Line 1 Error converting data type varchar to numeric.

This was my data that I entered following steps on another post here

update Product set ProdPrice = ‘price * 1.2’ where ProdName like ‘%monitor%’

Here is what the full table looks like: enter image description here