Expression 4: "F" Subscript, "K" , Baseline left parenthesis, "L" , "K" , right parenthesis equals StartFraction, "F" left parenthesis, "L" , "K" plus "h" , right parenthesis minus "F" left parenthesis, "L" , "K" , right parenthesis Over "h" , EndFractionFKL,K=FL,K+h−FL,Kh