Let us assume lowest score is = x.
We are given "The highest score on an algebra test was 42 points more than the lowest."
We took x for lowest score.
So, we need to write an expression for highest score in terms of x.
Therefore, the expression for highest score is = 42 more than x = x+42.
Is is also given that sum of both scores is 154.
We can setup and equation by using above statement.
Lowest score + Highest score = Total scrore.
x + x + 42 = 154.
Adding x and x we get 2x.
Therefore,
2x + 42 =154.
Subtracting 42 from both sides, we get
2x + 42-42 =154-42
2x = 112.
Dividing both sides by 2, we get
2x/2 = 112/2
x = 56.
Highest score = 56+42 = 98.
Therefore, highest score is 98 and lowest score is 56.