If x=(2+3t)(5_4t) find dx/dt when t=4/5sec?

To find dx/dt, we first need to expand the expression x=(2+3t)(5-4t):

x = 2(5) + 2(-4t) + 3t(5) + 3t(-4t)
x = 10 - 8t + 15t - 12t^2
x = -12t^2 + 7t + 10

Now, we can find dx/dt by taking the derivative of x with respect to t:

dx/dt = d/dt(-12t^2 + 7t + 10)
dx/dt = -24t + 7

Now, we can find dx/dt when t=4/5 sec:

dx/dt = -24(4/5) + 7
dx/dt = -19.2 + 7
dx/dt = -12.2

Therefore, dx/dt when t=4/5 sec is -12.2.