Recall that
distance = (speed)*(time)
we're given the speed and time. If we multiply them together, we get the distance
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The number 1.3 x 10^6 is in scientific notation. The coefficient 1.3 rounds to 1
This means "1.3 x 10^6" turns into "1 x 10^6"
Similarly, with the number 2.8 x 10^3, the coefficient 2.8 rounds to 3
The number "2.8 x 10^3" turns into "3 x 10^3"
When we multiply the numbers (1 x 10^6) and (3 x 10^3), we will
multiply the coefficients 1 and 3 to get 1*3 = 3
add the exponents: 6+3 = 9
So overall, the final answer is 3 x 10^9 indicating that it is choice C
(this is an estimate because we rounded the coefficients)