19.70-13=6.7
6.7/0.05=134
600+134=734
So in April she sent 734 text messages
Ignoring the "?" in your question:

If the "?" is a squared symbol that wasn't caught:

Use the quadratic formula

to get the solutions:

as you can see, the discriminant is negative, so the equation has no solution.
Answer:
1/2 log2
Step-by-step explanation:
I hope you understand