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 $4\frac{1}{3}$ 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*.