Find the critical value $t_{c}$ for the confidence level $c=0.90$ and sample size $n=19$. $=$ Click the icon to view the t-distribution table. $\mathrm{t}_{\mathrm{c}}=$ (Round to the nearest thousandth as needed.)

Step 1 ：To find the critical value $t_c$ for the confidence level $c=0.90$ and sample size $n=19$, we need to use the t-distribution table. The degrees of freedom will be $n-1 = 18$. The confidence level of $0.90$ corresponds to an alpha level of $0.10$. Since we are looking for a two-tailed test, we need to divide the alpha level by 2 to get $0.05$. We then look up this value in the t-distribution table to find the critical value.

Step 2 ：The critical value is approximately 1.7340636066175354.

Step 3 ：Final Answer: The critical value $t_{c}$ for the confidence level $c=0.90$ and sample size $n=19$ is approximately \(\boxed{1.734}\).