Using the Pressure & Temperature Graphs:

Q: Find the pressure at a depth of 1500 km.
A: Find 1500 on the bottom axis and follow the green line up to the black line on the pressure graph. Go left to find the pressure: 0.5 million atmospheres (atm).

Reverse the process......
Q: At what depth is the pressure 0.5 million atm?
A: Find 0.5 million atm and follow the green line to the black pressure line. Then drop all the way down and read the depth: 1500 km.

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Q: What is the temperature of the earth at a depth of 3500 km?
A: Find 3500 km on the bottom axis and follow the red line to the black temperature line. Go left and read the temperature: About 5400 °C.

Reverse the process........
Q: At what depth is the earth's temperature 5400°C?
A: Find the temperature of 5400°C. Follow the red line over to the black temperature line and drop straight down. Read the depth: 3500 km.