The answer is that the sister is 0.95 meters tall.
First of all, expand the left hand side:

Sum like terms:

Add 3 to both sides:

Subtract 3x from both sides:

So this is the solution. Every number smaller than 8 (excluded) is part of the solution of this inequality.
You would divide 28/3 because that's how many miles it would take. 28/3=9 1/3. Also, to help understand better, 3 miles is equal to 1 hour. So the equation would look like this: 3/1=28/?. To solve it like this, you'd divide 28/3 or 3*?=28. Whatever the answer is(9.33)you do it to the bottom. So 1*9.33. that equal 9 hours 20 min