Let x = the number of hours since 5 a.m.
Let y = temperature, °F
Let the total temperature change be modeled by the expression
y = ax + b
At 5 a.m., x = 0 and y = -9.4°F. Therefore
b = -9.4
When x = 6 hours, y = 2.8°F. Therefore
6a + b = 2.8
6a - 9.4 = 2.8
6a = 12.2
a = 2.0333
The expression is
y = 2.0333x - 9.4
Answer:
y = 2.0333x - 9.4
where
x = hours since 5 a.m.
y = temperature, °F
