Evaluate the given mathematical expression:

86 − 24 + 18 of 3 + 42 ÷ 2 − (35) + 15 = ?

The correct answer is 97.

To evaluate the given mathematical expression, we follow the standard order of operations (BODMAS / PEMDAS rule):

1. Brackets / Parentheses
2. Of / Orders (Exponents)
3. Division and Multiplication (from left to right)
4. Addition and Subtraction (from left to right)

Given expression:

$86-24+18\text{ of }3+42÷2-\left(35\right)+15$

Step 1: Simplify the "of" operation

$18\text{ of }3=18\times 3=54$

Substitute this back into the expression:

$86-24+54+42÷2-35+15$

Step 2: Perform the Division

$42÷2=21$

Substitute this result into the expression:

$86-24+54+21-35+15$

Step 3: Perform Addition and Subtraction from left to right

First, subtract 24 from 86:

$86-24=62$

Next, add 54:

$62+54=116$

Next, add 21:

$116+21=137$

Finally, simplifying the remaining net subtracted terms:

$137-40=97$

Hence, the final simplified value of the expression is 97.