Answer:
9 boards 
Step-by-step explanation:
2/3 of the porch= 6 boards 
so to figure out how much one third of the porch needs you find half of what it takes to fill in 2/3 of the porch and you get 3. 
so 3=1/3 of the porch 
then you simply do 3times 3 or 3+3+3 and you get 9
so it takes 9 boards to fill the whole porch 
 
        
             
        
        
        
Answer:
Amount of Niobium-91 initially
= 300/91 =3.2967mol
2040 years = 3 ×680 = 3 half-lives
therefore, amount left = 0.4121mol
mass of Niobium-91 remaining = 0.4121 ×91 =37.5g
Please give brainliest
 
        
             
        
        
        
Answer:
Y = -5
Step-by-step explanation:
The line needs to be parallel to the y-axis, which means it forms a 90° angle with the y-axis. This means the line we are looking for is a straight horizontal line. The line must pass through the point (-7, -5), but we can disregard the x value since we figured out that the line is perfecly horizontal, so it has no x value. The answer we are left with is y = -5, which is a horizontal line across -5 on the y axis. 
Hopefully you can understand my explanation :)
 
        
             
        
        
        
Answer:
10 miles is the correct answer