Given Are the First Three Terms of a Sequence That $10,15,20 , \ldots$

Multiple Choice

Given are the first three terms of a sequence that is either arithmetic or geometric. If the sequence is arithmetic, find a1
and d. If a sequence is geometric, find a1 and r.
- $10,15,20 , \ldots$

A) $\mathrm { a } _ { 1 } = 10 , \mathrm {~d} = 15$
B) $a _ { 1 } = 10 , d = 5$
C) $\mathrm { a } _ { 1 } = 10 , \mathrm {~d} = - 5$
D) $a _ { 1 } = 10 , r = 5$