Linux regular expression question:

Write a regular expression that you could use with egrep that will match all lines that contain a mathematical equation of the form value operator value = value where operator can be any mathematical operand (+-*/) and value is any numeric value. The equation does not have to be valid (for instance 9 * 10 = 11). Use the :digit: class where appropriate. Only write the regular expression. Do not include the egrep command and do not enclose it in single or double quotes.