It costs $0.07 to send a text message and $0.12 to send a picture on your cell phone. you spend $3.38 and send twice as many text messages as pictures. how many text messages did you send?

Let text message is m
it costs $0.07 to send a text message
so total cost of sending txt msg = 0.07m

Let picture is p
it costs $0.12 to send a picture
total cost of sending pics = 0.12p


You spend $3.38:
means: 0.07m + 0.12p = 3.38

AND

You send twice as many text messages as pictures:
means: m = 2p

solving these two equations together:
 
0.07m + 0.12p = 3.38
m = 2p

yields:

m = 26
p = 13


You sent 26 text messages and 13 pictures on your cell phone