(a) Find the t-value such that the area in the right tail is 0.10 with 25 degrees of freedom. (b) Find the t-value such that the area in the right tail is 0.05 with 30 degrees of freedom. (c) Find the t-value such that the area left of the t-value is 0.01 with 18 degrees of freedom.(d) Find the critical t-value that corresponds to 90% confidence. Assume 20 degrees of freedom.