To find the area of a Canadian football field, we start with the area of the American football field, which is given as \( 6.4 \times 10^4 \) square yards. We also know that the Canadian football field is 3,350 square yards larger.
First, we need to convert 3,350 into scientific notation.
3,350 can be expressed in scientific notation as: \[ 3.35 \times 10^3 \]
Now, we can add this to the area of the American football field.
To do this, we convert \( 6.4 \times 10^4 \) to have the same exponent:
\[ 6.4 \times 10^4 = 64.0 \times 10^3 \]
Now we can add: \[ 64.0 \times 10^3 + 3.35 \times 10^3 = (64.0 + 3.35) \times 10^3 = 67.35 \times 10^3 \]
Next, we convert \( 67.35 \times 10^3 \) back to standard scientific notation: \[ 67.35 \times 10^3 = 6.735 \times 10^4 \]
Now, we can express this in scientific notation to two decimal places: \[ 6.74 \times 10^4 \]
Thus, the area of a Canadian football field is \[ \boxed{6.74 \times 10^4} \text{ square yards.} \]