Question

how do you find the number of atoms of an element when it has both a subscript and a coefficient?
it is not possible with this information
multiply everything by the coefficient then add up the totals
multiply by the subscripts then add the coefficients
divide by the coefficient then subtract the totals
rewatch

Explanation:

To find the number of atoms with a subscript and coefficient, we multiply the coefficient by each subscript (for each element) and sum. The correct approach is "Multiply everything by the coefficient then add up the totals" as coefficients scale the entire formula's atom counts (subscripts show atoms per formula unit, coefficient scales the number of formula units). Other options are incorrect: it is possible, multiplying subscripts then adding coefficients is wrong, and dividing/subtracting is illogical.

Answer:

The correct option is: "Multiply everything by the coefficient then add up the totals"