Let's denote Owen's cleaning speed as \( r \) (in windows per minute). Since Greg is 1.7 times faster than Owen, his speed will be \( 1.7r \).
When Greg and Owen work together, their combined speed is:
\[ r + 1.7r = 2.7r \]
We know it takes them 39 minutes to clean 100 windows together.
The total work done (in windows) can be expressed as:
\[ \text{Work} = \text{Rate} \times \text{Time} \]
Thus, we can set up the equation:
\[ 100 = 2.7r \times 39 \]
Now we can solve for \( r \):
\[ 100 = 105.3r \] \[ r = \frac{100}{105.3} \approx 0.9496 \text{ windows per minute} \]
Now, we can find Greg's rate:
\[ 1.7r = 1.7 \times 0.9496 \approx 1.613 \text{ windows per minute} \]
Now we can find how long it would take for Owen alone to clean 100 windows. The time taken by Owen to clean 100 windows is given by:
\[ \text{Time} = \frac{\text{Work}}{\text{Rate}} = \frac{100}{r} \]
Substituting the value of \( r \):
\[ \text{Time} = \frac{100}{0.9496} \approx 105.3 \text{ minutes} \]
Thus, rounding to the nearest tenth, Owen would take approximately 105.3 minutes to clean 100 windows by himself.