Zhi Cong can type 90 words in every 2 minutes. He tends to type 9 words incorrectly every 10 minutes.

1. Convert the total time to minutes

$2 \text{ hours} = 2 \times 60 = 120 \text{ minutes}$

2. Calculate the total number of words typed in 120 minutes

Number of 2-minute intervals $= \frac{120}{2} = 60$
Total words $= 60 \times 90 = 5400$

1. Calculate the total number of incorrect words typed in 2 hours

Number of 10-minute intervals in 2 hours (120 minutes) = $120 \div 10 = 12$
Incorrect words = $12 \times 9 = 108$

2. Calculate the total number of correct words

Total words typed in 2 hours = $5400$ (from part a)
Correct words = $5400 - 108 = 5292$