If it would take billy an hour to race over to his girlfriend’s house and two hours if he went 20 mph slower, how far away does billy’s girlfriend 40 miles lol i guessed

Let d (miles) =  the distance to Billy's girlfriend's house.
Let v (mph) be Billy's speed when his time of travel is one hour.

Because distance = velocity * time,
therefore
time = distance/velocity.

Therefore
time = d/v = 1
v = d                     (1)

When Billy's speed is 20 mph slower, the time of travel is 2 hours.
Therefore,  the time is
d/(v - 20) = 2
Multiply each side by (v - 20).
d = 2(v - 20)          (2)

Substitute (1) into (2).
d = 2(d - 20)
d = 2d - 40
0 = d - 40
40 = d

40 miles

You're doing something i dont know how to do but search up on google slope calculator maybe that will get you there