Let Kirk's speed be R
Let Spock's speed be R + 30
So the time it took Spock to drive 240 miless = 240 / (R + 30)
And the time it took Kirk to drive 300 miles = 300/ R
So twice Spock's time = Kirk's time ....so....
2 [ 240 ] / ( R + 30) = 300 / R simplify
480 / (R + 30) = 300 / R cross-multiply
480 R = 300 (R + 30) simplify
480 R = 300R + 9000 subtract 300R from both sides
180 R = 9000 divide both sides by 180
R = 50 mph = Kirk's speed
R + 30 = 80 mph = Spock's speed
And Kirk's time = 300 / R = 300 / 50 = 6 hrs
And Spock's time = 240 / (50 + 30) = 240 / 80 = 3 hrs