Question

How do I solve this?

Answer 1

     y = abˣ
   20 = ab¹
   20 = ab
    b      b
20/b = a

 y = abˣ
 4 = (20/b)b²
 4 = 20b
20    20
¹/₅ = b

   y = abˣ
 20 = ¹/₅b¹
 20 = ¹/₅b
  ¹/₅     ¹/₅
100 = b

y = abˣ
y = 100(0.2)ˣ