Let P= $75, r=0.0054166, n= 40. In the future worth formula, F= P((1+r)^(n-1) -1) / r, it would yield a future worth of 3,247.16 at the age of 65. And the interest rate is I= (r^n-10)/(r-1). It yields an interest of 1.033
To do this, take Spencer's 85 pears and subtract Gwen's pears (p) to get the expression 85 - p.
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A1 = -7, an = 4(an - 1)
a2 = 4a1 = 4(-7) = -28
a3 = 4a2 = 4(-28) = -112
Therefore, the first six terms are -28, -112, -448, -1792, -7168, -28,672