Luas persegi panjang = L = 76 cm²

Lebar persegi panjang = $l$ = 0,4 dm = 4 cm

L = $p\times l$

76 = $p\times4$

$p=76\div4$

Panjang persegi panjang = $p=19$ cm

Keliling persegi panjang = $2\times\left(p+l\right)$

= $2\times\left(19+4\right)$

= $2\times23$

= 46 cm