To find the combined water capacity of the two water towers, we add their capacities together.
The first tower holds \( 7.35 \times 10^5 \) gallons, and the second tower holds \( 9.78 \times 10^5 \) gallons.
To add them together:
\[ 7.35 \times 10^5 + 9.78 \times 10^5 = (7.35 + 9.78) \times 10^5 \]
Calculating the sum:
\[ 7.35 + 9.78 = 17.13 \]
Now we express this in scientific notation.
Since \( 17.13 \) can be written as \( 1.713 \times 10^1 \), the combined total in scientific notation is:
\[ 1.713 \times 10^1 \times 10^5 = 1.713 \times 10^{1+5} = 1.713 \times 10^6 \]
Therefore, the combined water capacity in scientific notation is:
1.713 × 10^6
So, the answer is:
1.713 × 10^6 (1 point 7 1 3 times 10 to the 6th power)