A Financial Planner Wants to Compare the Yield of Income

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? __________________