Answer:
brooooo
Step-by-step explanation:
F U C K BRAINLY
b must be equal to -6 for infinitely many solutions for system of equations
and 
<u>Solution:
</u>
Need to calculate value of b so that given system of equations have an infinite number of solutions

Let us bring the equations in same form for sake of simplicity in comparison

Now we have two equations

Let us first see what is requirement for system of equations have an infinite number of solutions
If
and
are two equation
then the given system of equation has no infinitely many solutions.
In our case,

As for infinitely many solutions 

Hence b must be equal to -6 for infinitely many solutions for system of equations
and
Did you provide an picture ?!
Alright, so the area of one paper is 297mm*420mm=124740mm^2. Multiplying that by 6 due to 6 sheets, we get 748440mm^2. Converting mm^2 to m^2, since we know that 1000mm=1m, we simply do (1m/1000m)^2=1m^2/1,000,000mm^2. Our equation is now
748440mm^2*1m^2/1,000,000mm^2=0.748440m^2 by crossing out the millimeters. Lastly, since it's 80g/1m^2, we multiply our number by that to get 59.8752g