Answer:
1) Let's make sure we understand the word problem first. You send 12 texts a day, and your older sister sends more texts than you do. So overall you and your sister together send 26 text messages per day, which indicates subtraction.
26 - 12 = 14.
Your sister sends 14 texts per day.
2) So I'll assume you are connecting this to the problem above. Your father sends 19 messages per day, and u send 12 messages per day. HOW MANY MORE indicates subtraction.
19 - 12 = 7.
Your father sends 7 more texts than you do per day.
3) Alright, lets problem. The bill per week is $17.50, and there is 7 days in a week. So lets divide 7 by $17.50 since we need to know how much to save up per day.
17.50 ÷ 7 = $2.5.
You need to save $2.5 per day to pay the bill.