Alan

a + b = -5               (1)

a - b =  8                (2)

Add equations (1) and (2) term by term:

a+a + b +(-b) = -5 + 8

Simplifying

2a = 3

Divide both sides by 2 to get

a = 3/2   

You could substitute this back into either (1) or (2) if you also wished to find b.

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Ben:   $1400*75/(75+45)

Adam:  $1400*45/(75+45)

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If the pressure is constant you could use the fact that volume is proportional to temperature, so:

V₂ = V₁*T₂/T₁

Or, for the third, just use the fact that the three angles must sum to 180°

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What do you mean by "square rooted by 2"?

Net force, F = (7.87 - 3.08)*10⁴ N = 4.79*10⁴ N

Acceleration, a = F/mass  so  a = 4.79*10⁴/1.63*10⁴ m/s²  ≈  2.93865 m/s²

Use v² = u² + 2*a*s   where v = final velocity, u = initial velocity and s = distance travelled to get the final velocity.

i.e.  v = sqrt(64.5² + 2*2.93865*590) m/s

1 mole corresponds to 12 + 2*16 grams (i.e. 44 grams)    (12 for carbon,  16 for oxygen)

Hence there are 28/44 moles in 28 grams of CO₂  (28/44 ≈ 0.636)  

Depends on the context!  Do you have a specific example in mind?

There is a typo in my third line above.  It should read

At the beginning of the 3rd year it is worth  1250*0.9*0.9  → 1250*(0.9²)