Number of cookies = b
Number of cookies the family ate = 20
number of cookies left = ?
Number of cookies = Number of cookies ate + number of cookies that remained
b = 20 + number of cookies that remained
To get the number of cookies that remained, we'll subtract 20 from both sides:
[tex]\begin{gathered} b\text{ - 20 = 20 - 20 + number of cookies that remained} \\ b\text{ - 20 = number of cookies that remained} \end{gathered}[/tex]An expression showing number of cookies remaining:
[tex]\text{number of cookies that remained = }b\text{ - 20 }[/tex]