Qbasic to find area of four walls using Sub

DECLARE SUB Area ( L, B, H )
CLS
INPUT "Enter length'; L
INPUT "Enter breadth"; B
INPUT "Enter height"; H
CALL Area ( L, B, H)
END

SUB Area ( L, B, H )
A = 2 * H * ( L + B )
PRINT " Area of four walls="; A
END