C. 6 kg

Initial velocity \( u = 4 \, \text{m/s} \), Acceleration \( a = 5 \, \text{m/s}^2 \), Time \( t = 2 \, \text{s} \)

Final velocity: \(v = u + at = 4 + 5 \times 2 = 14 \, \text{m/s}\)

Change in momentum (impulse):
\(\Delta p = m(v - u) = 60\)

Substituting for \( v \): \(m(14 - 4) = 60\)

Simplifying: \(m \times 10 = 60\)

Thus, \(m = 6 \, \text{kg}\)