Solve.
-When making a telephone call using a calling card, a call lasting 4 minutes costs $\$ 2.10$. A call lasting 11 minutes costs $\$ 4.90$. Let $y$ be the cost of making a call lasting $x$ minutes using a calling card. Write a linear equation that relates cost $y$ to time $x$.
A) $y = 0.4 x - 6.1$
B) $y = 0.4 x + 0.5$
C) $y = - 0.4 x + 3.7$
D) $y = \frac { 5 } { 2 } x - \frac { 79 } { 10 }$

Question

Quizplus · Accepted Answer

To find the linear equation, we first calculate the slope ($m$) using the given points (4, 2.10) and (11, 4.90). The slope $m = \frac{4.90 - 2.10}{11 - 4} = \frac{2.80}{7} = 0.4$. Then, using one of the points and the slope, we can find the y-intercept ($b$) by plugging into the equation $y = mx + b$. Using the point (4, 2.10), $2.10 = 0.4(4) + b$, solving for $b$ gives $b = 0.5$. Thus, the equation is $y = 0.4x + 0.5$.

Solve -When Making a Telephone Call Using a Calling Card $2.10\$ 2.10$2.10

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-When Making a Telephone Call Using a Calling Card $\$ 2.10$