Answer: Tim sent 25 text messages
Explanation:
y=mx+c is being used
Since it increases by 0.15 each time so m=0.15 and the starting charge is 23.79 so c=23.79. We also know that his phone bill is 27.54 so y=27.54
Now this can be used to solve x
27.54 = 0.15x + 23.79
3.75 = 0.15x
25=x