The difference between each term is
-5, i.e. we know one of our terms is -5n. Now we just need to adjust it to get u1 correct. At n=1, -5n would give us -5 therefore we need to add 6 to get to 1. This gives us our equation:

Now we can work out the sum easily (we can use an equation using the above but personally I prefer the other one as it's less prone to mistakes):

We know n is 12, and we know u1 is 1, and we also know the difference is -5.
Substituting this in:
Answer:
1.544*10⁹ Linebackers would be required in order to obtain the same density as an alpha particle
Step-by-step explanation:
Assuming that the pea is spherical ( with radius R= 0.5 cm= 0.005 m), then its volume is
V= 4/3π*R³ = 4/3π*R³ = 4/3*π*(0.005 m)³ = 5.236*10⁻⁷ m³
the mass in that volume would be m= N*L (L= mass of linebackers=250Lbs= 113.398 Kg)
The density of an alpha particle is ρa= 3.345*10¹⁷ kg/m³ and the density in the pea ρ will be
ρ= m/V
since both should be equal ρ=ρa , then
ρa= m/V =N*L/V → N =ρa*V/L
replacing values
N =ρa*V/L = 3.345*10¹⁷ kg/m³ * 5.236*10⁻⁷ m³ /113.398 Kg = 1.544*10⁹ Linebackers
N=1.544*10⁹ Linebackers
It's might be.....180,000 I'm sure
Score = 6x+y
so 6x+y = xy
⇒ 6x = xy-y
⇒ 6x = y(x-1)
⇒ y = 6x/(x-1)
for x=0, y=0
x=1 , not possible
x=2, y = 12
x = 3, y = 9
x = 4, y = 8
x = 5, y = 7.5 (not possible)
x = 6 , y = 7.1 (not possible)
x = 7, y = 7
x = 8, y = 6.85 (not possible)
x = 9, y = 6.75 (not possible)...
Only five scores are possible.