Your mistake is that week 3 is twice of week 2 week2=x+5, twice of that is 2(x+5)=2x+10, you did not distribute the 2 to the 5 and you got 2x+5, that is your mistake
x is first week 2nd week is y 3rd is z
5 more the 2nd week than 1st week x+5=y
3rd week is double 2nd wee z=2y
total is 431
x+y+z=431 sub y=5+x and z=2y x+5+x+2y=431 sub 5+x for y x+5+x+2(5+x)=431 x+5+x+10+2x=431 4x+15=431 minus 15 4x=416 divide by 4 x=104 add 4 x+5=109 double 2*109=218
they sold 1st week: 104 2nd week: 109 3rd week: 218
