Answer:
Highest grade: 86
Lowest grade: 36
Step-by-step explanation:
Let the highest grade be h, lowest grade be l.
[tex]h = 50 + l \\ \\ h + l = 122 \\ h = 122 - l \\ \\ [/tex]
Therefore,
[tex]122 - l \: = 50 + l \\ 2l \: = 72 \\ l = 36 \\ \\ h = 36 + 50 = 86[/tex]