If the problem is 6r•s•4rt•10rst, then the answer is 240•r^3•s^2•t^2.

Step-by-step explanation:
Step 1:
Let us consider the given expression 
On Right Hand Side of equation,

Using BODMAS rule, we could get 2.4 as value.
Step 2:
Now let us consider the Left Hand Side of equation and solve it
which will be equal to 2.4.
Density = Mass/Volume => Volume = Mass/Density = 12/3.1 = 3.87ml