1. I’m not sure how you’ve been taught to factorise quadratics, but I was taught to multiply a by c, in this case 3*10 which is 30. Then draw out (3a-15)(3a-2) for the factors that add to get 17 and multiply to get 30. Then divide the one where both integers are divisible by 3. So it’ll turn out to be (3a-2)(a-5).
2. The same with 2, 11*-2 = -22, the factors that add to get -9 and multiply to get -22 are -11 and 2 (as -11+2=-9) so (11x-11)(11x+2) and then divide the divisible, so the answer’s (11x+2)(x-1)
3. the factors that add to get -2 and multiply to get -24 are -6 and 4, so (3y-6)(3y+4) then divide again (3y+4)(y-2)
You just have simple mistakes when it comes to mixing up signs, just write out your work carefully and you should be able to stop those mistakes. You can check your answers by solving for x, and then substituting it into your equation. if you get 0 you’re right