Hey there!
C₇H₉+ HNO₃ → C₇H₆(NO₂)₃+ H₂O
Our elements: C, H, N, and O.
Balance H.
Ten on the left, eight on the right. Add a coefficient of 2 in front of H₂O.
C₇H₉+ HNO₃ → C₇H₆(NO₂)₃+ 2H₂O
Balance N.
One on the left, three on the right. Add a coefficient of 3 in front of HNO₃.
C₇H₉+ 3HNO₃ → C₇H₆(NO₂)₃+ 2H₂O
This unbalanced H, let's increase the coefficient in front of H₂O from 2 to 3 to rebalance.
C₇H₉+ 3HNO₃ → C₇H₆(NO₂)₃+ 3H₂O
Balance O.
Nine on the left, nine on the right. Already balanced.
Balance C.
Seven on the left, seven on the right. Already balanced.
Our final balanced equation:
C₇H₉+ 3HNO₃ → C₇H₆(NO₂)₃+ 3H₂O
Hope this helps!