94. Random variables $X$ and $Y$ are independent. The variances of these variables are known: $D(X)=5 ; D(Y)=9$. Find the variance of the random variable $Z=2X-Y+5$.
S o l u t i o n. Using the properties of variance reflected in formulas (40), (41), and (42), we get

$$
D(Z)=D(2 X-Y+5)=2^{2} \cdot D(X)+(-1)^{2} \cdot D(Y)=4 \cdot 5+9=29
$$