This is not a MATLAB question. It doesn't even need fft or correlation. If you do FFt, you'll simply see two spikes, one for one signal and one for the other signal. It's just basic math. Since the period of one is 7 and the other is 9, what do you think the repeat period would be? Don't think about spectra or programming. Just think about things like least common multiple or whatever.
If you want MATLAB code to visualize the signal, here it is:
t = linspace(0, 63 * 4, 1000);
x = 4 * sin(2 * pi * t / 7) + 5 * sin(2 * pi * t / 9);
plot(t, x, 'b-', 'LineWidth', 2);
xlabel('t', 'FontSize', 15);
ylabel('x', 'FontSize', 15);
for k = 0 : 63 : max(t)
xline(k, 'Color', 'r', 'LineWidth', 2);
g = gcf;
g.WindowState = 'maximized'