3. For each of the following estimated models provide the simplest possible explanation of the effect of IQ (intelligent quotient has mean of 100) on EARNS (annual earnings in $). Hint: For models with logs use elasticities or semi-elasticities. (a) EARNS = 1000 + 500 x IQ. (b) EARNS = 20000 + 200 x IQ + 2 x 1Q2. (c) EARNS = -20000 + 50000 x In(IQ). (d) EARNS = 45000 + 10000 x d , where d = 1 if IQ > 100 and d = 0 if IQ