Explanation:
remember : calculations are usually done from left to right, but multiplications and divisions come before + and -.
and exponents come before multiplications and divisions.
and minus a negative number always turns into plus a positive number.
so,
3b²c - 2ad = 3×4²×2 - 2×3×-2 = 96 - -12 = 96 + 12 = 108
and
ac - bd/7 = 3×2 - 4×-2/7 = 6 - -8/7 = 6 + 8/7 = 7 1/7 ≈ 7.143