Max earns 1800 per month plus a comission of 3 % of his sales he wants to earn at least 3000 this month what amount of salws does max need this month

He earns 1800 so, 3000 minus 1800 is 1200, if u set this up as a proportional relationship you'll get  1200 = 3
                                      x      100

cross multiply the relationship, 1200 by 100 is 120,000, 3 by x is 3x, 3x=120,000            isolate the variable so you divide 3x by 3 and get 1x,
                                      what you do to one side you have to do to the other 
                                       so 120,000 divide by 3 is 40,000. If max wants to earn at least 3000 this month he will have to sell at least 40,000 dollars in items

Do the inverse operation