Answer:
<u><em>y = -190 cos(π t / 120) + 195</em></u>
Step-by-step explanation:
<em>General form of a sinusoidal function: y = A cos(Bt - C) + D
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<em>Now generally a cosine function starts at the maximum value, so to start at the minimum value, flip the cosine function by making it negative.
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<em>A is the amplitude of the curve and will be the radius of the ferris wheel. Therefore, A = 380 / 2 = 190 feet.
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2π / B is the period of the curve and will be the time to complete one full rotation. The time to complete one full rotation is given as 4 minutes. Convert this into seconds to get period = 4 minutes * (60 seconds / minute) = 240 seconds. Therefore, B = 2π / period = 2π / 240 seconds = π / 120.
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C/B is the phase shift, or horizontal shift of the graph. Since the negative cosine function already starts at the minimum value, there is no phase shift so C/B = 0, meaning C = 0.
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D is the vertical shift and will be the height of the center of the ferris wheel. Therefore, D = 195 feet.
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Your final function will be:</em>
<u><em>y = -190 cos(π t / 120) + 195</em></u>
The total number of gifts = x+y.
The inequality is:

Key chains cost $1, Magnets $0.50
Total Cost = x + 0.5y
Inequality is:

Without graphing you can solve system by using substitution:

This is one solution where the maximum x value is given.
So the most keychains that can be purchased is 16. However, because magnets are cheaper, more can be purchased as long as cost remains under 20.
If you solve both inequalities for "y", you get the upper and lower bounds for how many magnets can be purchased given a quantity of keychains.

This is complete solution which gives all possible combinations.
(Graph is Attached)
4(4x + 6) - 7 = 77 - 4x......distribute thru the parenthesis
16x + 24 - 7 = 77 - 4x ...simplify
16x + 17 = 77 - 4x ...addition property of equality....add 4x to both sides
16x + 4x + 17 = 77 ...subtraction property ...subtract 17 from both sides
16x + 4x = 77 - 17...combine like terms
20x = 60 ....division property....divide both sides by 20
x = 60/20
x = 3