An equation is a mathematical statement that two quantities are equal.
Equations can be used to represent and solve problems.
Sometimes part of an equation is unknown.
Unknown values can be represented by a variety of letters and/or symbols.
The commercial aired four times each hour for h hours.
The commercial aired 12 times in those h hours.
So, h groups of four equals 12.
Other equations in the same fact family could also be used to solve for h.
Shelly has yards of fabric.
She needs an additional f yards of fabric to have a total of 6 yards of fabric.
Other equations in the same fact family could also be used to solve for f.