Looks like you are on the right track.

I think the problem now might be to many (()).. The compiler is confused.

((8*Lint)+Ldec) * ((8*Lint)+Ldec)/ 4 / H / 1000

L8 = 8 * Lint
LT = L8 + Ldec
R = LT * LT /4 / H / 1000

Maybe???