[tex]perimeter= 144 \ cm\\ width : \ w= 30 \ cm \\ length: \ l= ?\\ \\Perimeter = 2 w + 2l \\ \\144=2 \cdot 30 +2l \\ \\ 144=60+2l[/tex]
[tex]2l=144-60 \\ \\2l=84 \ \ /:2 \\ \\ l=42 \ cm \\ \\Area = l\cdot w \\ \\A=42*30 =1 260 \ cm^2 \\ \\Answer : \ area \ of \ the \ computer \ monitor : 1260 \ cm^2[/tex]
