So, you are going to need to memorize the format y-y_1=m(x-x_1), just like how you need to memorize y=mx+b. Let me explain what y_1 and x_1 means. y_1 is the y value in the first point, which is where the one is from, or you can say (although it's not the correct mathematical term) the second number in the parenthesis. m is slope as you know from y=mx+b. x_1, sort-of like our y_1 is the x value of the first point, or the first number in the parenthesis.
Now that you know what each variable is, now you just need to plug in the numbers into the format: y-y_1=m(x-x_1).
You might be wondering, why is the answer y-3=4(x+2), I thought it was x minus x_1, not adding. Well you are correct, it just so happens to be that it is easier, and still correct to write x plus x_1 because x_1 is negative. Subtracting a negative is the same as adding so it is easier to write it that way.
