Anyone?? :)) please help

see explanation

Step-by-step explanation:

Given M is directly proportional to r³ then the equation relating them is

M = kr³ ← k is the constant of proportion

To find k use the condition r = 4 when M = 160, thus

160 = k × 4³ = 64k ( divide both sides by 64 )

2.5 = k

M = 2.5r³ ← equation of proportion

(a)

when r = 2, then

M = 2.5 × 2³ = 2.5 × 8 = 20

(b)

when M = 540 , then

540 = 2.5r³ ( divide both sides by 2.5 )

216 = r³ ( take the cube root of both sides )

= r , thus

r = 6

45 minutes

step-by-step explanation: