In order to calculate the original price of the radio we just have to do a rule of thirds, we know that the price payed was $50, and that it was 10% off from the original price, now we just have to to a simple rule of thirds, if $50 is the 90% how much is the 100%?
Add the five to each side. then square it to get rid of the square root 2x+13=(5+x)^2 2x+13=x^2+10x+25 2x=x^2+10x+12 x^2+8x+12=0 (x+6)(x+2) x+6=0 x+2=0 answers are -2 and -6, however, when pluging -6 in it doesnt work, so it is only -2.