Question 192689
Let  arithmetic  sequence  be  x,  x+d, x+2d.   sum  is  3x +3d=21,  or  x+d=7  (KEY)

multiply (x) (x+d) (x+2d) = 180
x^3+3dx^2+2d^2x=180  (KEY)

but  x+d=7,  therefore  x=7-d   (KEY)

substitution  and  simplyfing

-7d^2+163=0

d=4.8255   ANSWER

but  x=7-d,  x=7-4.8255 , x=2.1744  ANSWER

set  is  2.1744,  7,  11.8254   SUMMARY  ANSWER

check
2.1744 +(2.1744+4.8255)+(2.1744+4.8255+4.8255)=21  ok

2.1744 *  (2.1744+4.8255)*(2.1744+4.8255+4.8255) = 180  ok