A direct variation between IQ and Number of Antennae looks like this:
IQ = k*(Number of Antennae)
where k is the "constant of proportionality". Let's use our one data point (Number of Antennae=5, IQ=75) to find the value of k:
IQ = k*(Number of Antennae)
75 = k*5
75/5 = k
15 = k
Now we can find the IQ of a bee with 8 antennae:
IQ = k*(Number of Antennae)
IQ = 15*8
IQ = 90