Juliet is driving the same direction on a single highway for a road trip. When she starts her trip, she notices that she is at mile marker 225 and the mile markers are counting up as she drives. She is driving $75 \mathrm{mph}$. Which mile marker will she be at after 1.8 hours?

Step 1 ：Given that Juliet starts her trip at mile marker 225 and is driving at a speed of 75 mph.

Step 2 ：We need to find out which mile marker she will be at after 1.8 hours.

Step 3 ：We can calculate the distance Juliet will cover in 1.8 hours using the formula for distance which is speed multiplied by time. So, the distance is \(75 \times 1.8 = 135\) miles.

Step 4 ：Since she starts at mile marker 225, after driving for 1.8 hours, she will be at mile marker \(225 + 135 = 360\).

Step 5 ：Final Answer: Juliet will be at mile marker \(\boxed{360}\).