Answer:
 c. 30%
Step-by-step explanation:
The formula and the calculation of the annual rate of return is shown below: 
= Annual net income ÷ average investment 
where, 
Annual net income is $180,000
And, the average investment would be 
= (Initial investment + salvage value) ÷ 2 
= ($900,000 + $300,000) ÷ 2 
= $1,200,000 ÷ 2 
= $600,000
Now placing these values in the formula above 
So, the rate would equal to 
= $180,000 ÷ $600,000
= 30%