explaining infinity is a little complicated as i do not know what grade you are in so you get the complicated version(ps if you are not in grade 12 yet this will impress you teacher)
infinity is essentialy all numbers (i.e. no matter what number you give there are more after it, so infinity plus, minus, times or divided by anything is still infinity) but, and here is where it gets complicated, there are some infinities that are bigger than others for example there are more real numbers between 1 and 2 than there are the infinite mumber of whole numbers
see no matter how high you count in whole nubers there are more real numbers as all you need to do is make sure 1 digit is different and it is another number
x=1 and x=-3 so it is (x-1) and (x+3)
added together -1 and 3 equal 2 and when multiplied equal -3 so look for the equation with their product (-3) as the constant (no variable) and their sum (2) as the coeficient of the middle term
so the correct answer is b.
x^2 + 3x - x - 3
x^2 + 2x - 3