10b-45=3(b-15) plzz help

10b-45=3[b-15]
10b-45=3b-45
7b=0
b=0

His is also correct^
10b-45=3(b-15)
you need to (rainbow we call it) distribute the 3(b-15)
which becomes 3b-45.
10b-45=3b-45
add 45 from the right over to the left to make 0.
10b=3b
subtract the 3b from the right to the 10b on the left to make the right side 0.
7b=0
b=0 because anything that equals 0 must have one or the other of the multipliers equal 0.