Out of 45 times at bat, raul got 19 hits, find rauls batting average as a decimal rounded to the nearest thousandth

It can be written as an equation:

19 = x * 45    (x is the percentage we look for)
19 = 45x    / : 45 (both sides)
x = 4,2222     (after rounding it to the thousandth)

It means that Raul had 42,222% of hits.

Doublecheck it:

45 * 42,2% = 18,9999    (the difference of 0,0001 is because of the rounding before, but it's correct)