Ineed solving an=a1+(n-1)d and i'm suppose to solve for d. i need : )

The first thing to know is that "an" and "a1" are names with subscripts and are and different from multiplication.
 an = a1 + (n-1) d
 add -a1 to both sides
 an - a1 = a1 - a1 + (n-1) d
an - a1 = (n-1) d
d = (an-a1)/(n-1)

If gravity is one third on mars then weight also one third on mars

The skating rink rented 872 pairs of skates during april and may.why? : if the skating rink rented three times the pair of skates in april during may, they rented 654 skates. 218 x 3 = 654then, if they want to know how many they rented during both april and may, then you just add 654 (may) and 218 (april) to give you 872 pairs of skates for both months.654 + 218 = 872hope this !