In kickboxing, the force needed to break a board varies inversely with the length of the board. It takes Carson 18 pounds of force to break a board that is
4 feet long. How much force would he need to break a 20 foot long board? Enter number only, no units. Round to the nearest tenth if necessary.

The size of a certain cell is 2.5*10^-9m. another cell is 1.5*10^3 times larger. how large is the larger cell in scientific notation?

What is the value of x in the equation 2(x-4) = 4(2x + 1)?

Each person in an it department of 25 people works on at least one of 3 major projects: system security, program implementation, platform development. 10 people work on system security, 13 work on program implementation, and 12 work on platform development. 4 people work on system security and platform development, 5 people work on program implementation and platform development, and 2 people work on all three projects. how many people work on system security and program implementation?