Answer:
Liquid; melting.
Step-by-step explanation:
So what is being shown is a phase change diagram. Because we start at an atm of 1.5 (staying steady means that it doesn't drop so we always stay at 1.5 atm) and at a temperature of -150, the original state of matter is a solid. Next, we look at what happens when the temperature goes to 300 degrees, yet still maintaining the 1.5 atm. This means that it now turns into a liquid (based on placement on diagram). This means the matter after the temperature change was a liquid. And going from solid to liquid would be called melting.
Here's an example phase diagram so that you can rely on it in the future problems!