Witch expression is equivalent to 2x+3y-x-(8+1)

Danielle earns a 7.25% commission on everything she sells at the electronics store where she works. she also earns a base salary of $750 per week. what were her sales last week if her total earnings for the week were $1,076.25?

Ageologist had two rocks on a scale that weighed 4.6 kilograms together.rock a was 0.5 of the total weight.how much did rock a weigh?

How many sides does a regular polygon have if each exterior angle measure is 45 degrees explain your answer, i really don't understand this.