HARD Algebra Math Question!!

Find the focal length of the magnifying glass if you can see the butterfly clearly when your eye is 5.5 cm away from the glass and the glass is 25 cm away from the butterfly.
The formula is " 1/s + 1/t = 1/f
a. Focal length is 30.5
b. Focal length is 4.5
c. Focal length is 4.2

1/5.5 + 1/25 = 1/f
0.1818 + 0.04 = 1/f
0.2218 = 1/f
4.508 = f
Answer b

1/5.5 + 1/25 = 1/f
25+5.5 = 137.5/f = 30.5
f = 137.5/30.5 = 4.5 cm
Answer b.

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