A financial planner wants to compare the yield of income and growth mutual funds. Fifty thousand dollars is invested in each of a sample of 35 income and 40 growth funds. The mean increase for a two-year period for the income funds is $900. For the growth funds the mean increase is $875. Income funds have a population standard deviation of $35; growth funds have a population standard deviation of $45. At the 0.05 significance level, is there a difference in the mean yields of the two funds? What is the Null Hypothesis?