std_msgs::Duration multipliation

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Hi I want to calculate a distance. Therfore I have a std_msgs::Duration t and want to calculate:

d*d = t*t * w*w;

with w is the speed of sound (for now as a float). The error I get is:

no match for ‘operator*’ (operand types are ‘const Time {aka const std_msgs::Time_<std::allocator<void> >}’ and ‘const Time {aka const std_msgs::Time_<std::allocator<void> >}’)
 d1_2 = t1*t1*omega*omega;

I think I have to convert the duration into a float. But I don't know how to do.