Consider a data consisting of 10 observations $x_1, x_2, \ldots, x_{10}$, whose mean is 5 and variance is 7 . If the mean and the variance of the first 8 observations $x_1, x_2, \ldots, x_8$ are 4 and 3.5 , respectively, and $x_9 < x_{10}$, then the value of $3 x_9+2 x_{10}$ is $\_\_\_\_$ .