Answer:
m > -5
Explanation:
Divide your inequality by the coefficient of m, which is -3. Doing that requires you reverse the comparison symbol:
(-3m)/(-3) > (15)/(-3)
m > -5
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The comparison symbol is reversed whenever an inequality is multiplie or divided by a negative number. You might be able to see why when you look at the relation between a couple of integers:
-2 < -1
2 > 1 . . . . . . multiply the above by -1
Multiplying by a negative number effectively reflects the comparison across the center of the number line. As we know from looking in a mirror; reflection reverses left and right, so numbers that were farther to the right (more positive) are now farther to the left (more negative).