f = @(x) (x^2 + 3);

a = 7;
b = 12;
n = 10;
h = (b - a) / n;

s = 0.5 * (f(a) + f(b));
for i = 1:n-1
    s = s + f(a + i * h);
end

I = h * s;
disp("I: " + I);