First you would find the 10% discount of $109, which is equal to 90% of $109 or .9*$109 = $98.10.
You would then take $98.10 and find the 12% discount with is equal to 88% of $98.10 or .88*$98.10 = $86.33
Then you would add a 6% sales tax would would be 106% of $86.33 or 1.06*$86.33 = $91.51
Thus, she did not have enough to buy, and was $1.51 short.