It costs $0.05 to send a text message and $0.10 to send a picture on your cell phone. you spend $4 and send five more text messages than pictures. how many text messages, x, and pictures, y, did you send?

The first thing we must do for this case is to define variables:
 x: text messages
 Y: pictures
 We write the system of equations:
 0.05x + 0.10y = 4
 x = y + 5
 Solving the system we have:
 x = 30
 y = 25
 
 you send:
 30 text messages
 25 pictures