One day, River writes down the numbers 1, 2,, 999 What is the sum of all the digits that River wrote down? And what is the number of all the digits River wrote down

Iam trying to solve a linear equation for the shoe size of someone 84" tall taking into consideration example 1 is 69" tall with a shoe size of 9 and example 2 is 72 inches tall with a shoe size of 11. i understand that the equation should be y=mx+b and that on the graph the answer is (3,2) but i just don't understand how to create the equation to solve for 84-inches and 60-inches tall questions. after two days, i need .

Write the equation in logarithmic form 8^x=64

Using only odd number for numerators write two different subtraction problems that have a difference of 3/4