Have been randomly reminded how much ✨classic science fiction✨ consists of Boys' Own textbook word problems.
"Star-Colonel Dick Davely set off from Earth toward Aldebaran at 5 times the speed of light using his ship's awesome Atomic Warp Drive. At the same time, Zong the Evil Ethnic Alien set off from Aldebaran toward Earth at only 3.5 times the speed of light, due to his race's inferior technology, to make good on his cowardly threats to photon-beam the White House.
"'Dick!' Betsy Bimbo, Dick Davely's hometown sweetheart, cried needily. 'Oh, Dick, with both ships in motion, we'd need to know the precise instant their paths will cross to time the firing of our forward laser-howitzer, or miss entirely and condemn the Earth to photon bombardment!'
"'Actually,' Dick grinned condescendingly, 'Zong's as good as dead already! Why, with the all-American power of simple algebra—'"