Factor the expression 20k+50 explain every step you did

So, to factorise something you are taking out the highest common factor. Here, 10 is an example of the highest common factor (I'll refer to this as HCF)

10 (2k+5)

Everything inside the brakets is multiplied by what's directly next to it (if there is a negative sign, then that is included). So, 10 x 2k = 20k and 10 x 5 = 50

10 (2k + 5) is the factorised version of 20k + 50