Need help with homework; new to programming in general

One has 50 samples of water from various streams. You measure those samples for dissolved oxygen. If the sample falls below 5mg/l then the stream will be listed as impaired. Make a program

that imports the excel file from the Matlab folder to a matrix called 'DO'

Loops through each of the samples in DO and checks to see if it is classified as impaired or unimpaired

Using column 3 in DO (a new column) assign a value of O for impaired and 1 for unimpaired

Export this file to the matlab folder

   edit.. where I'm having problems is getting my data to come into the excel spread sheet. I know I must set up a conditional where if the data the second column (format of the excel sheet is (stream, oxygen present) in (a1,b1), but I need a program that will generate a value of zero or one in cells C1:C50, deciding whether the sample is impaired or unimpaired..