The result of raising any number to a power cannot be zero, because it implies an exponent of minus infinity, so I assume that the zero should be 1, which tells us that the exponent is zero.
Working on this basis, -4t(cos(3t)-(4/3)sin(3t))=0, which has t=0 as one solution. The contents of the brackets can also be zero, so cos(3t)=(4/3)sin(3t), and tan(3t)=3/4. 3t=0.6435 radians making t=0.2145. In degrees t=12.29. So t=0 or 0.2145 or 12.29 degrees. There are other solutions because of the periodic nature of the trig functions, so t=60n or t=12.29+60n degrees where n is an integer or t=n(pi)/3 or t=0.2145+n(pi)/3 radians.