First you have to figure out the distance she traveled. On Saturday, the distance x took her 1.8 hours to drive, on Sunday the same distance x took her 2 hours to drive. We know that when you take the distance (x) and divide by the time needed to travel (1.8 and 2 hours) you will get the speed she traveled. We also know that the difference between her speed on sat vs sunday was 5 mph.
So you can set up the equation like so.
(x/1.8) - (x/2) = 5. This means that the speed on Saturday (x/1.8) minus the speed on Sunday (x/2) is 5 mph.
Now to solve for x. Find the common denominator, just multiply 1.8 and 2 which is 3.6. So the equation becomes:
(2x/3.6) - (1.8x/3.6) = 5 With a common denominator, subtraction becomes simple. So the equation becomes:
0.2x/3.6 = 5 To solve for x, multiply both sides by 3.6. the equation becomes:
0.2x=18. Divide both sides by 0.2, so then x = 90.
Now the x we said represents the Distance traveled. So she traveled 90 miles. On saturday her speed was 90/1.8 which is 50 mph, on sunday her speed was 90/2 which is 45 mph. 50 and 45 are 5 apart just as the question asked. So you can now confirm that she traveled 45 mph on sunday.