The wave equation of 2 waves are given by $\;x_{1}=4 \sin 3t\; mts\;$ and $\;x_{2}=3 \cos 3t \;mts \;.$ The amplitude of the resulting wave is

Question

$(a)\;5\;mts\qquad(b)\;6\;mts\qquad(c)\;7\;mts\qquad(d)\;1\;mts$