Answer :
Step 1
Get the equation for the cost/charge of the cab for a given number of miles
[tex]\begin{gathered} C=0.4x+5 \\ \text{Where C = cost} \\ x\text{ = number of miles} \end{gathered}[/tex]Step 2
A) Determine the cost function C, of riding the cab for m miles.
[tex]\begin{gathered} \text{The equation is} \\ C=0.4x+5 \\ \text{but x = m miles} \\ \text{Hence,} \\ C=0.4m\text{ + 5} \end{gathered}[/tex]Step 3
B) What is the cost of a 21-miles taxi cab ride
[tex]\begin{gathered} C=0.4(21)+5 \\ C=8.4+5=\text{\$}13.4 \\ \end{gathered}[/tex]Step 4
C) How far can you ride if only you have $19
[tex]\begin{gathered} C=0.4x+5 \\ \text{\$19}=0.4x+5 \\ 0.4x=19-5 \\ 0.4x=14 \\ \frac{0.4x}{0.4}=\frac{14}{0.4} \\ x=\text{ 35 miles} \end{gathered}[/tex]Hence, you can ride 35 miles if you only have $19