Which of the following is the smallest ratio?

$\frac{5}{6}, \frac{7}{9}, \frac{11}{12}, \frac{13}{18} $

The force (in pound-force) needed to keep a car from skidding on a curve varies directly with the weight of the car (in pounds) and the square of its speed (in miles per hour [mph]) and inversely with the radius (in feet) of the curve. Suppose 6125 pound force is required to keep a 2750 pound car, travelling at a speed of 35 mph, from skidding on a curve of radius 550 feet. How much pound-force is then required to keep a 3600 pound car, travelling at a speed of 50 mph, from skidding on a curve of radius 750 feet?

What smallest positive number should be subtracted from 2 and 3 so that 4 is the third proportion to them?

The ratio of the number of boys in a school to the total number of boys and girls in that school is 7 ∶ 17. If the number of boys in that school is 1099, then how many girls are there in that school?