Confidence Intervals · Superchallenge problem

Two groups of $10$ are measured: group 1 has $\bar x = 20$, $s = 3$; group 2 has $\bar x = 22$, $s = 4$. The two groups are then treated as ONE sample of $20$ from a single population. Find the upper end of the $95\%$ $t$ interval for its mean ($t^* = 2.093$, $19$ degrees of freedom). Give your answer to the nearest hundredth.