Given :
Human blood should have around 1.04 kg/L platelets.
A blood sample of 4.01 milliliters is collected from a patient to be analyzed for a platelet count.
To Find :
The expected mass in grams of platelets in the blood sample.
Solution :
1 L of human blood contains 1.04 kg of platelets.
So, amount of platelets is 1 ml blood is :

Mass of platelets in 4.01 ml blood is :

Hence, this is the required solution.
There are a couple of ways todetermine if a reaction is exothermic or endothermic. Endothermic meaning that heat is added to the reaction to make the reactants interact and exothermic meaning heat is released during the reaction between the two reactants.
In endothermic reactions you can find a triangle above the arrow.
410g Ag
2.3*10^24 atoms
1 molcule Ag- 6.02g*10^3