If we represent Tobin's speed as x, we can write her opponent's speed as
x-2 (since Tobin is 2 more than them). In addition, since it's in miles per hour, and 45 minutes is 3/4 of an hour, we can say that 3/4ths of her speed in miles per hour is how long the race is, so (3/4)(x-2)=distance of race. In addition, since it only took Tobin 30 minutes, and 30 minutes is half an hour, x/2 (half of her miles per hour) is the length of the race, so (3/4)(x-2)=(1/2)x. Expanding it, we get 3x/4-6/4=x/2. Subtracting x/2 (or 2x/4) from both sides, we get x/4-6/4=0 and by adding 6/4 to both sides we get x/4=6/4. Multiplying 4 to both sides, we get that x=6=Tobin's speed in miles per hour
