faye=f
martin=m
john=j
f=18
f-x
m+x
f-x=7
so subsitute f=18 for f in f-x=7
18-x=7
add x to both sides
18=7+x
subtract 7 from both sides
11=x
faye gave 11 stickers to martin
f now equals 7 so forget that f equaled 18 before so f=7
j=2f
we know that f=7 so we subsitute f=7 for f in the equation
j=2(7)
j=14
john has 14 stickers
before
f=18
m=?
j=14
after
f=7
m=?+11
j=14