10meters=1000cm
1000-210=890
Mary has 890 centimeters of thread left on the reel.
-(-2x-6y=-16)
2x+6y=16
4x-6y=-58
Y's cancel out, then add the rest
6x=-42
divide both sides by six
x=-7
plug x into any previous equation
2(-7)+6y=16
-14+6y=16
6y=30
y=5
Step-by-step explanation:







option C