#### Answer

$\displaystyle \frac{203}{3}=67\frac{2}{3}$ quarts

#### Work Step by Step

We know that we need to use $7\frac{1}{4}$ quarts of additive for each tank of fuel. Therefore, if we have $9\frac{1}{3}$ tanks, the amount of additive must be the product of these two numbers. First, we estimate the result by rounding to the nearest whole number:
$Additive\approx 7*9=63$ quarts
Now, we get the precise answer:
$Additive=\displaystyle 7\frac{1}{4}*9\frac{1}{3}=\frac{29}{4}*\frac{28}{3}=\frac{29*28}{3*4}=\frac{29*7}{3}=\frac{203}{3}=67\frac{2}{3}$ quarts