If the bacteria is tripling every 10 minutes, that means the "rate of increase" on that period is 200%, so if say the current amount is "c", 200% of "c" is just 2c, so c + 2c is 3c, a tripled amount.
X^2-5x+5x-25 (multiply (x-5) with (x+5))
X^2-25 ( -5x+5x =0)
The answer is 7.14%
Your ruler measuring centimeters has lines for each centimeter. The rule for error is anything between 6.5 and 7.5 is considered 7cm. So the degree of error is plus or minus .5cm.
Your aim is 7cm so you divide your error of .5 by your target measurement. .5/7= 7.14 percent.