HI. I need help with the example below:

An engineer in charge of a production process that produces a stain for outdoor decks has designed a study to test the research hypotheses that an additive to the stain will produce an increase in the ability of the stain to resist water absorption. The mean absorption rate of the stain without the additive is 40 units. The engineer places the stain with the additive on 50 pieces of decking material and records sample average of 36.5 and standard deviation 13.1. Is there significant evidence in the data to support the contention that the additive has decreased the mean absorption rate of the stain using 1% significance level (use rejection region approach)?