QBASIC to find Area of 4 walls using FUNCTION

DECLARE FUNCTION Area ( L, B, H )
CLS
INPUT "Enter length"; L
INPUT "Enter breadth"; B
INPUT "Enter height"; H
PRINT "Area of 4 walls = "; Area ( L, B, H )
END

FUNCTION Area ( L, B, H )
Area = 2 * H * ( L + B )
END FUNCTION