25c(quarters) x 12 = $3.00
If theres 28 coins, and 12 are quarters, then that means theres 16 coins left to use for dimes.
10c(dimes) x 16 = $1.60
$3.00 + $1.60 = $4.60
Therefore, there are 12 quarters and 16 dimes.
Hope this helps! Feel free to ask any questions.