He may be wrong. If he was wrong, this is the example.
0 < -10x
If we were to divide both sides by -10, even though the answer would be undefined or just end up as zero, it is just a common rule to always flip the sign whenever you divide or multiply by a negative.
Don't quote me on it, but I think I'm right.
Hope this helped!
57 cubic thingie so the last one
1/5x-2/3x15 =30
0.2x-30/3=30
0,2x-10=30
0,2x-10+10=30+10
0,2x=40
0.2x x5=40x5
x=200
If you do cross multiplication you would get
60x=1800
x=30 to be exact so the answer is choice d