A taxi charges a fixed 4 dollars and then 2.5 dollars for each kilometre.

Step 1. The equation. $y = 2.5x + 4$.

Step 2. Twelve kilometres. $y = 2.5 \times 12 + 4 = 30 + 4 = 34$ dollars.

Step 3. A fare of 29 dollars. $2.5x + 4 = 29$, so $2.5x = 25$ and $x = 10\ \text{km}$.

Step 4. On the graph. $2.5$ is the slope: the line rises $2.5$ dollars for each kilometre. $4$ is where the line meets the y-axis, the fare for a ride of $0\ \text{km}$.