New phone plan = $294
New phone plan compared to old phone plan (in savings) = $3.50 per month
12 months in a year, therefore multiply 12 with 3.50 and you get the total number of savings in the entire year
12 (months in a year) × $3.50 (savings per month) = $42 (per year in savings)
Since Kym saved $42 a year, and we know that Kym's new plan costs $294 a year, simply add $294 (new phone plan) and $42 (savings per year) to get the price of the old phone plan.
$294 (new phone plan) + $42 (savings a year) = $336 (old phone plan per year)
Now, since you want to find the monthly payment, simply divide $336 (old phone plan on a yearly payment) by 12 (months in a year).
$336 (old phone plan per year) ÷ 12 (months) = $28
Kym paid $28 per month under her old phone plan.