im worried for my grades.

i want to go to poly, im G2 in english and science. But i'm G1 in math and MTL (Chinese.) i'm secondary 2 so i still have a chance to move up, even though i'm good in maths and understand well i don't see my G1 turning into a G2, I do know about the 75% rule. my three questions are must I get 75 percent for all or 3/4 of the subjects and if i do go to g2 for math and then have 3/4 g2s (english,math and science) am i able to qualify for N(A) and if i score well for WA3 and EOY am i able to qualify for G2 streaming.