So Kristina already owes $5.00 for the first 600. She went over 242 texts and each one costs $0.05.
To determine what she owes for the over texts you would multiply 242 and 0.05.
242*0.05 = $12.10 is the price for the over texts.
After figuring out the price for the over texts, you would add the primary $5 to the $12.10.
5 + 12.10 = $17.10
So in total, Kristina would have to pay $17.10 for this month.
Hope i helped E: