working with iterations of y?

if i have a code of something like

x = -10:0.1:10; f1 = trapmf(x,[-2 0 0 2]); f2 = trapmf(x,[3 6 6 9]);

and I want to work with these plots for each y-intercept from 0 to 1, how would I do it?

for example, I want to find the x-intercepts of f1 and f2 for every y of 0:0.005:1; (since x = 201x1);

I think if there's a way to save all the values with a for loop, I can make this work? something like

for i = 1:201

    y(i) = [x(i),f1(i)]
end

any thoughts are appreciated.. thank you.