Briana saved $1.80
Further explanation
Algebraic expressions in mathematics are a combination of coefficients, numbers, variables, constants and arithmetic operations such as addition, subtraction, multiplication, and division.
Purchasing a backpack that cost $45 with a sales promotion of 20% off
![\tt 20\%* \$45=0.2* 45=\$9](https://img.qammunity.org/2021/formulas/chemistry/high-school/r43fgq0o7cmzpdxsizthoylcf9rkqa0bx1.png)
![\tt cost=\$45-\$9=\$36](https://img.qammunity.org/2021/formulas/chemistry/high-school/ghrgatvuaml6sfyznd5qww71j4u2603d7n.png)
Purchasing a backpack that cost $42 with a sales promotion of 10% off
![\tt 10\%* \$42=0.1* 42=\$4.2](https://img.qammunity.org/2021/formulas/chemistry/high-school/y6y48sv86v09nes4p2wmkpscinhnlcbccv.png)
![\tt cost=\$42-\$4.2=\$37.8](https://img.qammunity.org/2021/formulas/chemistry/high-school/yrwrlouoibjlgo1j0tiumtaoadezspafjn.png)
Briana saved :
![\tt \$37.8-\$36=\$1.8](https://img.qammunity.org/2021/formulas/chemistry/high-school/krxgs1vvvwn1pm8ethf8cvjgpe6t09b8ra.png)