@cryptoaops: I'm pretty sure they are. To the first question:

add 21 to both sides and divide both sides by -4 to get **x=-5**

To the second question: subtract 12 on both sides and multiply both sides by 3 to get **m=18**

To the third question: distribute and subtract 10 on both sides and divide both sides by -12 to get **z=-4**

To the last question: combine like terms and add the numbers and add 5 to both sides and divide both sides by 7 to get **a=5**

sniped -_-