Mr. Henderson paid a total of $98.40 for phone service and $79.20 for garbage pickup last year. To find his average cost per month for these two services, we need to divide the total amount he paid by the number of months in a year.
Since there are 12 months in a year, we can divide the total amount Mr. Henderson paid for phone service and garbage pickup by 12 to find his average cost per month. This is calculated as follows:
Average cost per month = (98.40 + 79.20) / 12
Average cost per month = 177.60 / 12
Average cost per month = $14.80
Therefore, Mr. Henderson's average cost per month for phone service and garbage pickup last year was $14.80. This means that, on average, he paid about $14.80 per month for these two services.