Hello!
Let’s look at the acronym PEMDAS:
P - parentheses
E - exponents
M - muliplication
D - division
A - addition
S - subtraction
Now we can apply this order of operations to the given equation. Because there are no parentheses, we begin by simplifying the exponents:
90 - 5² x 3
90 - 25 x 3
Now we can move on to multiplication:
90 - 25 x 3
90 - 75
Finally, we can skip down to subtraction:
90 - 75
15
Using PEMDAS order of operations, the correct answer is 15.
I hope this helps!
