DSE 2012 Econometrics doubt

[Econenthusiast]

Q38 of DSE 2012

Suppose you have 500 observations and you regress wage (measured in rupees per hour) on experience in the labour market, exper (measured in years), and on experience in the labour market squared, (exper^2).
Your estimated OLS equation is
wdage = 3.73+ 0.298 exper - 0.0061 exper^2
              (0.35) (0.041)         (0.0009)
where the standard errors are in brackets. The estimated equation implies
(a) The returns to experience is strictly increasing
(b) The returns to experience is strictly diminishing
(c) The returns to experience is constant
(d) Experience has no statistically signicant effect on wage

Could someone explain how we arrive at the answer that the returns to experience is strictly diminishing ?

[Econenthusiast]

Also if anyone could reason out why the answer to this question ( from DSE 2016)  is D.

Instead of estimating a true cost function, which is described as quadratic, where costs are regressed on an intercept, output and a quadratic term in output, a researcher estimates a linear function by regressing costs on an intercept and output. The estimates from the linear cost function are likely to:

(A) Have autocorrelated residuals
(B) be a biased estimate of marginal cost, even though there is no exact linear relationship between the linear and quadratic terms in output
(C) both (A) and (B)
(D) neither (A) or (B)

[sumit raturi]

Just double differentiate the function with respect to experience, it will come out as a negative number and hence diminishing returns

[Econenthusiast]

Thanks a lot Sumit!. You have any clue on how to go about the 2016 question ?