Find the principal square root of the given number.

$$49$$

Solve the given equation. Check the solution.

$$9 x^2-16=0$$

Solve the given equation by factoring. Check the solution.

$$\frac{25}{49}-r^2=0$$

Find the given product.

$$(3 k+8)(3 k+8)$$

Solve the given equation. Check the solutions.

$$7 b(b-4)=0$$

Marta has a bag of $8$ marbles. There are $3$ red marbles, $2$ blue marbles, $2$ white marbles, and $1$ black marble. If she picks one marble without looking, what is the probability that it is either black or white?

F $\frac{1}{8} \qquad$ H $\frac{3}{8}$

G $\frac{1}{4} \qquad$ J $\frac{5}{8}$