You can obtain #16.4 oz# cereal for #$2.79#.

That implies #25oz# will cost #$x#.

If we keep the #oz# on one side and the #$# on the other, we can build an equation to solve for the unknown #x#.

We start with two expressions that we want to have similar results. These are mathematical expressions of the first two lines we wrote above.

#16.4oz -> $2.79#

#25oz -> $x#

To complete the equation we can divide one expression by the other and equate them:

#(16.4oz)/(25oz) = ($2.79)/x#

#(16.4cancel(oz))/(25cancel(oz)) = ($2.79)/x# simplify and then cross multiply

#16.4x = 25*$2.79#

#16.4x = $69.75

#x=$4.25#

To check the answer for correctness, #25oz# is about #1/3# more than #16.4oz#. That means if the approximately #$3.# were also increased by #1/3#, we should add about another #$1.# So the total will be around #$4.#

Then you would receive #$5.00 - $4.25 = $0.75 or 75 cents# change from a fiver.