C seems to make the most sense, logarithmic and exponential functions are not gradual, and a step function just wouldn't fit in my eyes.
Cost of month plan = $40
Cost of minutes used = $0.45 after 700 minutes
Total cost = $48.10
Let x be the total minutes used
Total cost = 40 + 0.45(x - 700)
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Form the equation and solve x
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40 + 0.45(x - 700) = 48.10
40 + 0.45x - 315 = 48.10
0.45x - 275 = 48.10
0.45x = 48.10 + 275
0.45x = 323.10
x = 323.10 ÷ 0.45
x = 718
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Answer: John had used 718 mins this month
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(6.0 x 10^5) x (3.0 x 10^4) = (6 x 3) x 10^(5 + 4) = 18 x 10^9 = 1.8 x 10^10
Step 1. Factor out common terms in the first two terms, then in the last two terms.
2x^2(x - 5) -5(x - 5)
Step 2. Factor out the common term x - 5
(x - 5)(2x^2 - 5)
3/30=9/v
3×3=9
30×3= 90
v=90
