Answer:
m = 20
Step-by-step explanation:
given m is directly proportional to r³ , then the equation relating them is
m = kr³ ← k is the constant of proportionality
to find k, substitute m = 160 when r = 4 into the equation
160 = k × 4³ = 64k ( divide both sides by 64 )
2.5 = k
m = 2.5r³ ← equation of proportion
when r = 2 , then
m = 2.5 × 2³ = 2.5 × 8 = 20
