Every variable in your code is a scalar, including x and y. When you call plot using scalars, no line will be plotted, and you will only see the value if you specify a marker, like 'o':
v0 = (125/3.6);
g = 9.81;
t = 7.4535;
h = 60.4972;
theta = (pi/0.1944);
x = v0*t*cos(theta);
y = h - ((g*t.^2)*1/2)+(v0*t*sin(theta));
plot(x,y,'o');
To plot a line, x and y need to contain multiple elements. For example,
v0 = (125/3.6);
g = 9.81;
t = linspace(1,7.4535,100);
h = 60.4972;
theta = (pi/0.1944);
x = v0*t*cos(theta);
y = h - ((g*t.^2)*1/2)+(v0*t*sin(theta));
plot(x,y);
