please answer all four pleaseee on the file its 100 points plzz answer it asap I also give brainliest

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?

Given abc find the values of x and y. in your final answer, include all of your calculations.

Random variables x poisson~ ( a) ,y poisson ~ ( a) . x and y are independent. if 2 1, 2 1. u =2x+ y-1, v=2x- y +1. find: ) cov (u ,v ).