Globalpetrolprices.com is a website that compares utility bills for households and businesses. It has been observed that Denmark, German and Italy have the highest household electricity costs. Suppose Italy's electricity pricing is as follows: Each household bears a minimum of 50$ fixed charge and an additional 0.78$ for each unit of electricity consumed by the household.

Based on the above scenario, please answer the following instructions:

(i) Formulate a linear function for the electricity pricing based on the consumption. Please clearly define each variable.

(ii) How does the average rate of change in electricity price with consumption impact a consumer's monthly bill? Answer by calculating the average rate of change.