Extraction and Grouping Common Factors help!

Hey guys, I am really confused with this work, I missed some time from college as I was ill and missed the work. Can anyone help me?

Question 1 says, use appropriate methods to completely factorise the following expression by extraction and grouping of common factors.

(A) 12a2b + 15ab2

(B) 10ab - 8ax + 15b - 12x

Question 2 says, solve a quadratic equation by factorising and one by the formula method.

a mojor leak is discovered on the surface of oil storage tank in the workshop. the supervisor decides that the best solution to this is to weld a reinforcement sheet of metal on the leaking area.

after taking measurements, the following conditions are decided.

- the are of rectangular sheet of metal should be 24000mm2

- the length of the sheet should be 10mm greater than the width

Calculate the dimensions of the reinforcement sheet.

What would be the dimensions if the area of the sheet was reduced wo 21987mm2?

Could someone please explain how to to this for me? Thank you!