Let the number of text messages be represented by X.
Then the total cost of David's cell phone adds up to
[tex]50.00 + 0.45x[/tex]
Since the total cost of David's phone equals $91.40, we get the following equation.
[tex]50.00 + 0.45x = 91.40[/tex]
Subtract 50 on both sides
[tex]0.45x = 41.40[/tex]
Divide both sides by 0.45
[tex]x = 92[/tex]
Therefore David has send 92 text messages.
