A: Superheat is a constant-pressure process, so you move horizontally to the right until you hit your target temperature line, then drop straight down vertically to read enthalpy from the axis — never follow the temperature curve. For the logarithmic pressure axis, use the saturated property table to find the saturation temperature at your pressure (e.g., 150 psia → 105°F), then use that temperature line on the chart to pin your point more precisely. And remember: H₃ = H₄ because the expansion process is isenthalpic, so once you find state 3 you have state 4 for free.

A: That is not the quality equation — quality is x = (H – HF) / HFG, or equivalently (H – HF) / (HG – HF). The formula you wrote doesn't make physical sense: quality is a fraction between 0 and 1, and that expression wouldn't behave that way. Make sure this is crystal clear before exam day.