help me pleeeeeeease

[tex]P = l + l + b + b[/tex]
[tex]P = 2(2a + 3) + 2(8a - 12)[/tex]
[tex]\boxed{\sf{P=20a-18}}[/tex]
[tex]P = 20(3) - 18[/tex]
[tex]P = 60 - 18[/tex]
[tex]\boxed{\sf{P = 42 cm}}[/tex]
[tex]P = (3b + 7) + (7b - 2) + (7b - 2)[/tex][tex]\boxed{\sf{P = 17b+3}}[/tex]
[tex]P = 17(6) + 3[/tex]
[tex]P = 102 + 3[/tex]
[tex]\boxed{\sf{P = 105 \: m}}[/tex]