Zack used these steps to solve this equation:

Three-fourths y + 5 = negative three-fourths y minus 9. Step 1: StartFraction 6 Over 4 EndFraction y + 5 = negative 9. Step 2: StartFraction 6 Over 4 EndFraction y = negative 14. Step 3: (StartFraction 6 Over 4 EndFraction) StartFraction 6 Over 4 EndFraction y = negative 14 (StartFraction 6 Over 4 EndFraction). Step 4: y = negative 21.

When Zack checked his solution, it didn’t work. What was his mistake?