Carlos walks 4 miles every night for exercise. its takes him exactly 64 minutes to finish his walk.
a. assuming he walks at a constant rate write an equation that represents how many miles y carlos can walk in x minutes

Ok, so if he walks 4 miles per 64 minutes, or 4 miles/64 min which will reduce to 1 mile/ 16 min,  then the numbers of miles he walks in a given number of minutes would be

1/16 * number of minutes

The question states we represent miles with y and number of minutes with x, so...

y = 1/16x

So let's check it...

How many miles (y) in 64 minutes (x)

y = 1/16x
y = 1/16 * 64
y = 64/16 = 4 miles 

Yep! It checks!