Answer
${$313.39}$/month
Work Step by Step
This constitutes $75\%$ of the population of Mexican-born immigrants in the US or
$0.75\times 7.8=5.85$ million people.
The average that each remits in a month is equal to the total amount of remitted money divided by the number of people.
$\frac{$22,000,000,000}{5,850,000}$ = ${$3760.68}$/year.
Divided by $12$ months in a year, we get ${$313.39}$/month.
