Use $m = \dfrac{y_2 - y_1}{x_2 - x_1}$ with your two points, where $x$ corresponds to time $t$ and $y$ corresponds to temperature $T$.

After finding the slope $m$, write $T(t)=mt+b$. Substitute one of the known points $(t, T)$ into this equation to solve for $b$.

Type each option as a separate function: y=-3.5x+87, y=-3.5x+80, y=3.5x+80, and y=-42x+80.

For each function, open its table (tap the gear/table icon) and add $x=2$ and $x=14$. Look for the line whose table gives $y=80$ when $x=2$ and $y=38$ when $x=14$; that equation is the correct model.

The temperature $T$ depends on time $t$, so write the information as points $(t, T)$:

• Two minutes after the reaction begins: $t=2$, $T=80$ gives the point $(2, 80)$.
• Fourteen minutes after the reaction begins: $t=14$, $T=38$ gives the point $(14, 38)$.

These two points lie on the graph of the linear function $T(t)$.

Use the slope formula with points $(2,80)$ and $(14,38)$:

So the temperature is changing at $-3.5$ degrees Celsius per minute (decreasing by $3.5$ degrees each minute).

Use slope-intercept form $T(t) = mt + b$, with $m = -3.5$ and one of the points, say $(2, 80)$:

Substitute $t=2$ and $T=80$:

So the equation is

which matches answer choice A.