What number gives a result of -4 when 10 is subtracted from the quotient of the number and 5

Which one ? is the answer and how to find this answer

Someone answer asap for ! michele pushes a box d meters across a floor. she uses a force f, in newtons, to push the box. she pushes the box for t seconds. the formula p = fd/t calculates the power, p, in watts, that it takes for michele to complete the task. solve the formula for d.

At noon a tank contained 10cm water. after several hours it contained 7cm of water. what is the percent decrease of water in the tank?