Use element-wise operators (beginning with a dot) instead of matrix operators. E.g.,
y1=(0.02049/0.4)*x;
y2=(0.59*60./(1+(1.331./(sqrt(0.0631*x./(74.45-x))).^3)));
y3=(0.59*60./(1+(1.331./(sqrt(0.0631*x./(74.45-x))).^3)))-(0.02049/0.4)*x;
y4=(0.02049/0.4)*x-(0.59*60./(1+(1.331./(sqrt(0.0631*x./(74.45-x))).^3)));