having trouble plotting 2 graphs

hello, i am having some trouble superimposing 2 graph. when i run the following script, matlab says that the vectors are not equal (i am guessing this is because one is in months while another is in years??). can someone please point out what i am doing wrong?

n = 18*12+1;

balance([1,n],1)=[2000;0];

for b1=2:n

      balance(b1)=(balance(b1-1)*(1+(5.5/1200))+200);

end

for year=2:22

cost(year)= cost(year-1)+(cost(year-1)*0.08);

end

totalcost= cost(19)+cost(20)+cost(21)+cost(22);

figure(1)

x=1/12*[1:216];

y1=balance;

y2= ones(1,216)*totalcost;

plot(x,y1,'k', x,y2,'b')

Answer 1

[Walter Roberson]

n = 18*12+1; -- is it even or odd?

x=1/12*[1:216]; -- does it have an even number of elements or an odd number of elements?