Sure, let's solve this step by step.
1. Step 1: Determine Current Grades and Required Average
Emma has the following grades from her first three tests: 68, 74, and 86. She needs her average grade to be 80 or higher.
2. Step 2: Calculate Current Total of Grades
First, let's add up Emma's grades from her first three tests:
[tex]\[
68 + 74 + 86 = 228
\][/tex]
So, the total of Emma's grades so far is 228.
3. Step 3: Calculate the Required Total for Four Tests
To achieve an average of 80 over four tests, we need to calculate the total score required for four tests. The required average is 80, so for four tests, the total score needed is:
[tex]\[
80 \times 4 = 320
\][/tex]
The total score Emma needs to achieve an average of 80 is 320.
4. Step 4: Determine the Minimum Fourth Test Grade
We need to find out the minimum grade Emma needs on her fourth test to reach the total of 320. We can do that by subtracting the total of her current grades from the required total:
[tex]\[
320 - 228 = 92
\][/tex]
Emma must score at least 92 on her fourth test to achieve an average of 80.
Therefore, the correct answer is:
OD. 92
