What is the volume of a brick that has a length of 20 cm a width of 6 cm and a height of 5 cm

All you do is multiply the numbers. So 20 x 6 x 5 = 600 cm

You just multiply the values because you are finding the volume of a rectangular prism. 20*6*5=20*30=600cm^3 Hopefully this helps!

For the number 7, begin by solving for k.
Remember your discriminant rules:
k is greater than 0, there are 2 real solutions
k is equal to 0, there is one real solution
k is less than 0, there are no real solutions

On number 8, solve for a, and then figure out the number of solutions using the rules above.

Hope this helps!