The following information applies to questions 6 and 7. Two cannons are arranged vertically, with the lower cannon pointing upward (towards the upper cannon) and the upper cannon pointing downward (towards the lower cannon), 200m above the lower cannon. Simultaneously, they both fire. The muzzle velocity of the lower cannon is 25 \mathrm{~m} / \mathrm{s} and the muzzle velocity of the upper cannon is 55 \mathrm{~m} / \mathrm{s}. How long after the cannons fire do the projectiles collide?
Answer Choices
A. 2.2 \mathrm{~s}
B. 2.5 \mathrm{~s}
C. 3.6 \mathrm{~s}
D. 6.7 \mathrm{~s}
E. 8.0 \mathrm{~s}
