This works:
y = [-1 -0.3 -4 -0.1 0.25 0.4 0.2 0.9];
x = [0 0.1 0.2 0.3 0.4 0.5 0.6 0.7];
yx = find(y>0,1,'first'); % Choose 1st ‘y’ Point >0
y0 = 0;
x0 = interp1(y(yx-1:yx),x(yx-1:yx),y0); % Find Zero Cross Between Bracket Points
figure(1)
plot(x, y)
hold on
plot(x0, y0, 'bp')
hold off
grid
