We're learning about mirrors, concave, convex and stuff like that.
Ive been reading ahead because i dont have the greatest teacher and i came across a small problem.
Ive circled it here.
I dont understand how they got from that step to the next and where the 42 came from.
Did they round off the 10.5 to 11 then break it down.. then times the 7 by 6?
i know my theory is wrong but thats the only thing i could think of for it to possibly equal that.