You paid $600 for a new guitar. Your guitar costs $40 more than twice the cost of your friend's guitar. How much did your friend's guitar cost?

Cost of your guitar = $ 600

Let your friend's guitar's cost be = n

According to the question =

Your guitar costs $ 40 more than twice the cost of your friend's guitar which is n, but your guitar's cost is $ 600.

So, the linear equation for this will be =

= 2n+$40 = $600

= 2n = $600-$40

= 2n = $ 560

= n = $ 560/2

= n = $ 280

Thus, the cost of your friend's guitar is $ 280.