Question 148623
If you draw where you have driven so far, north 30 miles then east 45 miles and then draw a line from where you stopped back to the point you started, you'll see that you have drawn a right triangle. The two 'short sides' are 30 and 45. 

The shortest distance 'home' is the third leg (the hypotenuse) of the right triangle. How are the lengths of those three legs related mathematically? Pythagorean theorem!

{{{a^2 + b^2 = c^2}}}
You've been given a= 30 and b=45. Just plug in the values and take the square root  of their sums.
{{{sqrt(30^2 + 45^2) = c }}}
{{{sqrt(900 + 2025) = c}}}
{{{sqrt(2925) = c }}}
{{{54.08 = c }}}