How to predict future generations from heritability
"How would I plug those numbers into the breeders equation?"  You would use those fertility rates in calculating the selection differential (S), which would essentially be a weighted intelligence average of the reproducers minus the population average (reproducers+non-reproducers).  So, if the population starts wih 100 IQ and those with 125 IQ produce 2.1 and those with 75 IQ produce 1.9 and those two groups are equally populated, the weighted intelligence avg of reproducers becomes (125*2.1+75*1.9)/4=101.25.  The selection differential is then 101.25-100=1.25.  Response is 1.25*.5=.625.  IQ moves to 100.625.  In your example, S=10.  That is, (x*2.1+y*1.9)/4-100=10, where x is the avg IQ of the above average group and y is the avg IQ of the below average group, assuming the two groups are equally populated.