the given expression is,
f(x) = I -3x + 12 I - 7
f(x) + 7 = 3x - 12
f(x) + 7 = 3 (x - 4)
from the above expression it is clear that
there is the horizontal translation of 12 units is wrong
the horizontal translation is 4 unit.
so the first option is incorrect
thus, the answer is option A
the English teacher took 4 unit translation in left and he wrote he took the horizontal translation of 12 unit., thus this was the mistake that the teacher did.