if a fourth plant produces 400 widgets in 60 days, which statement is true?

the complete question in the attached figure

the statements are
1) It makes less than plant B
2) It makes the same as plant A
3) It makes more than plant C

we know that
analyzing the graph

plant A
for x=40  y=100
for x=50   y=200
that means 
the production in 10 days is 100 widgets
then
the production in 60 days will be 6*100----> 600 widgets
so
plant A production  > plant fourth production
plant fourth production < plant A production

plant B
for x=40  y=0
for x=60   y=100
that means 
the production in 20 days is 100 widgets
then
the production in 60 days will be 3*100----> 300 widgets
so
plant B production  < plant fourth production
plant fourth production > plant B production

plant C
for x=20  y=0
for x=40   y=100
that means 
the production in 20 days is 100 widgets
then
the production in 60 days will be 3*100----> 300 widgets
plant C production  < plant fourth production
or 
plant fourth production > plant C production

therefore 

the answer is 
3) It makes more than plant C