a)
x+3x+7y = 41
4x + 7y = 41
2(3x+7y) = 66
6x+14y = 66
answer
4x + 7y = 41
6x+14y = 66
b)
solve
4x + 7y = 41
6x+14y = 66
divide 2nd equation by 2
3x + 7y = 33
now you have
4x + 7y = 41
3x + 7y = 33
------------------subtract
x = 8
4x + 7y = 41
4(8)+ 7y = 41
32 + 7y = 41
7y = 41 - 32
7y = 9
y = 9/7
3x = 3(8) = 24
7y=7(9/7) = 9
answer
Length =9
width = 24