According to the PMBOK® Guide, specifically within the Control Costs process, the Cost Performance Index (CPI) is a measure of the cost efficiency of budgeted resources, expressed as the ratio of earned value to actual cost.

To find the Actual Cost (AC), we use the standard Earned Value Management (EVM) formula for CPI:

$$CPI = \frac{EV}{AC}$$

Given Data:

CPI = 0.92

Earned Value (EV) = US$172,500

Calculation steps:

Rearrange the formula to solve for AC: $AC = \frac{EV}{CPI}$

Substitute the values: $AC = \frac{172,500}{0.92}$

Calculate the result: $172,500 \div 0.92 = 187,500$

The actual cost of the project is US$187,500.

Performance Analysis:

A CPI of 0.92 (which is less than 1.0) indicates that the project is over budget.

Specifically, for every dollar spent on the project, only 92 cents of work was actually accomplished.

This is confirmed by the fact that the Actual Cost ($187,500) is higher than the value of the work performed ($172,500).

Analysis of other choices:

Choice A (US$158,700): This is the result of multiplying $172,500 \times 0.92$, which is mathematically incorrect for finding the AC.

Choice B (US$172,500): This is simply the EV; it would only be the AC if the CPI were exactly 1.0.

Choice D (US$245,600): This figure is not supported by the data provided in the formula.