Answer: Option A. -> x, + and =
Answer: (a)
Let us check all the options one-by-one.
From option (a).
3+2 x 1 = 7
By interchanging the signs, from the options. We get,
⇒  3 x 2 + 1=7 (using VBODMAS rule)
⇒  6 + 1 =7 ⇒ 7 = 7
∴ LHS = RHS
As an option (a) gives us a correct answer, there is no need to check the remaining options.

Answer: Option A. -> - and +
Answer: (a)
Let us check all the options one by one.
From option (a),
65 - 40 + 11 = 36
⇒  76 - 40 = 36
⇒ 36 = 36
⇒ LHS = RHS
So, option (a) is correct and hence there is no need to check remaining options.

Answer: Option D. -> ÷, x, x
Answer: (d)
8 ÷ 4 x 6 x 5
= $8/4$ x 6 x 5
= 2 x 6 x 5
= 60

Answer: Option B. -> + - x
Answer: (b)
Given, 7 * 7 * 2 * 1 = 12
Let us check all the options one by one.
From option (a),
putting the signs in given equation, we get
7 x 7 - 2 ÷ 1 = 12
⇒ 7 x 7 -2 = 12
⇒ 49 - 2 = 12
⇒  47 = 12
⇒ LHS ≠ RHS
So, option (a) is incorrect.
From option (b),
putting the signs in given equation, we get
7 + 7 - 2 x 1 = 12
⇒ 7 + 7 -2 = 12
⇒ 14 -2 = 12
⇒  12 = 12
Hence, option (b) is correct and there is no need to check remaining options.

Answer: Option D. -> x ÷ =
Answer: (d)
Since, 16 x 6 ÷ 4 = 24
⇒ $96/4$ = 24
⇒  24 = 24

Answer: Option A. -> ÷ x - =
Answer: (a)
Since, 9 ÷ 3 x 3 - 3 = 6
⇒ 3 x 3 - 3 = 6
⇒ 9 - 3 = 6
⇒  6 = 6

Answer: Option B. -> O
Answer: (b)
L ? K K K = 24
According to the question,
7 + ? + 4 + 4 + 4 = 24
⇒ ? = 24 - 19= 5=0
Hence, O is the missing symbol in the given.

Answer: Option B. -> = x +
Answer: (b)
From option (b).
24 = 4 x 5 + 4
⇒ 24 = 20 + 4
⇒  24 = 24

Answer: Option B. -> x - ÷
Answer: (b)
Since, 8 * 6 * 96 * 2 = 0
⇒  8 x 6 - 96 ÷ 2 = 0
⇒ 48 - 48 = 0

Answer: Option C. -> 15
Answer: (c)
According to the question,
? =  7 - 10 × 5 ÷ 6 + 4
from the question by changing the symbols, we get
= 7 + 10 ÷ 5 × 6 - 4 (using VBODMAS rule)
=7 + 2  × 6 - 4
= (7 + 12) - 4
= 15