Pls help me thanks !!

In simplified exponential notation, the expression a^2•a^-3•a 1/a 0

X^2/100+y^2/25=1 the length of the major axis is: a)5 b)10 c)20

Item 1 which question could the expression 1000n answer? let n = the number of gallons of gas used. how many miles per gallon did the car get driving 1000 miles? let n = the number of grams of food needed for each dog. how many grams of food are needed to feed 1000 dogs? let n = the number of people at the show. how many empty seats were there at the show if there are 1000 seats at the theater? let n = the number of seats at the theater. how many empty seats will there by if 1000 people come to the show?