Question 974782
v = f(t) = −2.606t + 131.8 
solve for t
−2.606t = v -131.8
t = -(v - 131.8) / 2.606
now interchange t and v
v = -(t - 131.8) / 2.607, therefore
f-1(t) = -(t - 131.8) / 2.606
f-1(t) = (131.8 - t) / 2.606
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f-1(61.8) =  (131.8 - 61.8) / 2.606
f-1(61.8) = 26.861089793 approx 26.86