Answer:
let the grade points be a,b,c
a+b+c=258
b=c+10( since she noticed that on tests two and three,she scored 10 points fewer).
Lcm of 60 and n = 420
Stated: n <90 and a multiple of 6
420/60 = 7 thus n must be a multiple of 7
Therefore n =42 or 84
