For the first line divide both sides by x^2.
2x = 3
For the second line the minus sign for 36b^2 means the factors are opposite signs. The minus sign for the 2abx portion means the factors forming the largest product will have the negative sign. The factors of 10a^2x^2 are 2ax and 5ax. The factors of 36b^2 are 4b and 9b. Because of the foil process the 4b*5ax =20abx and 2ax*9b =18abx which gives the needed center term with a 2abx if subtracted so 4b gets the negative sign
(2ax-4b)(5ax+9b)=0 is the factored form.
Solving for x we have 2ax-4b = 0
x=4b/2a The first answer
For the second factor we have
5ax + 9b = 0
x = -9b/5a The second answer.