The formula you have given here is for the volume of a cylinder. It should read

.
First, to find r, the radius, divide the diameter by two (since the radius is the distance from the circumference to the centre and the diameter is the distance from any point on the circumference to the opposite point (through the centre))
r = 8/2 = 4
Now we can calculate this.

If your answer needs to be in litres, one cubic centimetre = one millilitre.
603 cm3 = 603mL = 0.603 L
Is one of the answer choices no solution because that’s what I got.
Answer:
10.31 pounds
Step-by-step explanation:
First, we multiply 1.3 x 2 because he is gaining 1.3 for the next TWO weeks.
1.3 x 2 = 2.6
Now, add 7.71 + 2.6 because that is the weight he started with.
7.71 + 2.6 = 10.31
Her brother will weight 10.31 pounds if he is 7.71 lbs and continues to gain 1.3 pounds each week for two weeks.