Answer :

Scryt
At first you may get confused but look at those numbers carefully :)

as you see first result is divisible buy one of the product (second product in all cases is unknown)
so let's check where it will lead us :)

[tex]6/2=3[/tex]

[tex]12/3=4[/tex]

[tex]20/4=5[/tex]

[tex]30/5=6[/tex]

[tex]42/6=7[/tex]

Now you can clearly see that every number was multiplied by number 1 higher than itself. 
[tex]2*(2+1)=6[/tex]

[tex]3*(3+1)=12[/tex]

[tex]4*(4+1)=20[/tex]

etc...

it means that after equation sign there should be [tex]90[/tex] because 

[tex]9*(9+1)=90[/tex] :)