Answer:
13
Step-by-step explanation:
there is a rule that says that if you add any 2 sides, it should be more than the third. 9+21 is greater than 13. 21+13 is greater than 9. 13 is the only number which if you add 9 to it it will be greater than 21. 12 will equal 21, but it still wont work.
hope this helps :))
The relevant formula that we can use in this situation is:
v = v0 + at
where v is the final velocity, v0 is the initial velocity
= 20 km/hr, a is acceleration at 3.4 m/s^2 and t is time at 20 seconds
First convert v0 to m/s, v0 = 5.56 m/s
v = 5.56 m/s + 3.4 m/s^2 * 20 s
v = 73.56 m/s
Then convert back to km/hr:
<span>v = 264.82 km/hr</span>
Since the formula for the base of the cylinder is

, multiplying that by 10 we get

. Hope this helps!