First let's set up an equation: 35+0.05t.
35 is the phone rate per month plus the number of texts (t) times 0.05 (cost of 1 text)
Now we can find the amount of texts she sent each month.
March
35+0.05t=72.60
-35 -35
0.05t=37.60
------ -------
0.05 0.05
t=752
April
35+0.05t=65.85
-35 -35
0.05t=30.85
------ -------
0.05 0.05
t=617
She sent 752 texts in March and 617 texts in April.