{m=N[1/(1 - ((1 - a/((h - 20) (s - 11)))^ceil(h*v*3*10^-5)) *((1 - b/((h - 20) (v - 19 - s)))^ceil(h*v*1.5*10^-5)) )/3]} with h = 4200 ; v = 1200 ; s = 350 ; a = 69 ; b = 69