Owen paid $9.20 for 6 pencils and a pen. a pen cost twice as much as a pencil. (a) how much did a pencil cost? (b) how much did a pen cost? can you me with the model?

6x+1y=9.20 (x=pencils since he bought 6 pencils, y=pen since he bought one pen)
2x=y (the cost of two pencils equals to one pen since a pen costs twice as much)

now you just solve with substitution

6x+1(2x)=9.20
6x+2x=9.20
8x=9.20
x=1.15 (now you know that one pencil costs 1.15 dollars, now substitute that into the other equation)

2(1.15)=y
2.30=y (now you know then pen costs 2.30 dollars)

so your answer is
a) $1.15
b) $2.30