Answer:
-1
Step-by-step explanation:
Here we use the equation

Taking points (0,4), (1,2)
Substituting the point (0,4) , we will get

Substituting (1,2) we will get

So we have

Therefore , required equation is

62 because 90 minus 15, minus 13, is equal to 62
The school year would be 1981-1982