Answer:
She sold 20 american flags and 8 mexican flags.
Explanation:
In order to solve this we first have to do an equation, we will represent the american flag with the letter x, the mexican flag with y, so the amount of flags sold will be x+y=28, that would be our first equation, and the second will be 15x+20y=460.
We have both of out equations so now we just clear from x from the first one to get:
x=28-y
and insert that as value of x in the second one:
15x+20y=460
15(28-y)+20y=460
420-15y+20y=460
5y=40
y=8
Since y=8 we know that x= 20