Try this:
x_line = [7020 0];
y_line = [0 250000];
x_curve = [5620 4850 4290 3600];
y_curve = [0 100000 200000 300000];
b_line = polyfit(x_line, y_line,1); % Fit ‘line’
y_line2 = polyval(b_line, x_curve); % Evaluate ‘line’ At ‘x_curve’
x_int = interp1((y_line2-y_curve), x_curve, 0); % X-Value At Intercept
y_int = polyval(b_line,x_int); % Y-Value At Intercept
figure(1)
plot(x_line, y_line)
hold on
plot(x_curve, y_curve)
plot(x_int, y_int, '+r') % Plot Intercept Point
hold off
