Answer:
The
of a substrate will be "10 μM".
Explanation:
The given values are:

![[Substract] = 40 \ \mu M](https://tex.z-dn.net/?f=%5BSubstract%5D%20%3D%2040%20%5C%20%5Cmu%20M)

Reaction velocity, 
As we know,
⇒ ![Vo=\frac{K_{cat}[E_{t}][S]}{K_{m}+[S]}](https://tex.z-dn.net/?f=Vo%3D%5Cfrac%7BK_%7Bcat%7D%5BE_%7Bt%7D%5D%5BS%5D%7D%7BK_%7Bm%7D%2B%5BS%5D%7D)
On putting the estimated values, we get
⇒ 
⇒ 
⇒ 
On subtracting "40" from both sides, we get
⇒ 
⇒ 
Step 
<u>find the mass of a single washer</u>
Divide the total mass by the number of washers


Step 
<u>Convert kg to mg</u>
we know that

so

therefore
<u>the answer is</u>

...because this notation increases the convenience in using the numbers