The highest temperature on Sunday was 8°F and the lowest temperature was -3°F. What is the difference between the highest and lowest temperatures?

What the problem is asking

You are comparing two temperatures, one above zero and one below zero. The “difference” means how far apart the numbers are on the number line.

Subtract the lowest from the highest

Highest temperature: $8^\circ\text{F}$

Lowest temperature: $-3^\circ\text{F}$

Compute the difference: $$ 8 - (-3) = 8 + 3 = 11 $$ So the temperatures are $11^\circ\text{F}$ apart.

Quick number-line check

From $-3$ up to $0$ is $3$ degrees, and from $0$ up to $8$ is $8$ degrees. Together, $3 + 8 = 11$ degrees.