Mathematics

Mathematics

Problem

The surface area

S

of a cube with edge length

a

is

S=6a^{2}

. During an experiment, the edge is increasing at

1.5\,\text{cm/s}

while the surface area is increasing at

108\,\text{cm}^{2}/\text{s}

. What is the edge length

a

(in cm) at that instant? a)

12

b)

9

c)

6

d)

5

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