=(B8-VLOOKUP(B8,E9:H17,1,TRUE))*VLOOKUP(B8,E9:H17,4,TRUE)+VLOOKUP(B8,E9:H17,3,TRUE)
B8 is your K5
E9:h17 is the following data you provided:
$0--------50,000----0--------10%
50,000----75,000----5,000----11%
75,000----100,000---5,500----12%
100,000---125,000---9,000----13%...