Answer: $9
Step-by-step explanation:
Let the cost for adults be a
Let the cost for students be b.
The first van transported 2 adults and 5 students and cost $77. This will be:
2a + 5b = $77
The second van transported 2 adults and 7 students and cost $95. This will be:
2a + 7b = $95
2a + 5b = 77 ...... equation i
2a + 7b = 95 ........ equation ii
Subtract equation ii from I
-2b = -18
b = 18/2
b = $9
An student cost $9
Put the value of b into equation i
2a + 5b = 77
2a + 5(9) = 77
2a + 45 = 77
2a = 77 - 45
2a = 32
a = 32/2
a = 16
An adult costs $16
You started out with 260, and increased to 430.
The amount you increased was (430 - 260) = 170
170 is (170/260) = <em>65.4%</em> of what you started with.
============================
Another way:
The new amount is (430/260) of the old amount.
430 / 260 = 1.654 = 165.4%
The original amount was 260.
You started with 100% of it.
You ended up with 165.4% of it.
That's an increase of 65.4% .
A) The constant of proportionality in this proportional relationship is 
B) The equation to represent this proportional relationship is y = 0.2x
<h3><u>Solution:</u></h3>
Given that,
The amount Naomi pays each month for international text messages is proportional to the number of international texts she sends that month
Therefore,
This is a direct variation proportion

Let "y" be the amount that Naomi pays each month
Let "x" be the number of international texts she sends that month
Therefore,

y = kx -------- eqn 1
Where, "k" is the constant of proportionality
Thus the constant of proportionality in this proportional relationship is:

<em><u>Last month, she paid $3.20 for 16 international texts</u></em>
Therefore,
y = 3.20
x = 16
Thus from eqn 1,

Substitute k = 0.2 in eqn 1
y = 0.2x
The equation would then be y = 0.2x