The number of inversions for a slider crank mechanism is

The number of degrees of freedom of a planar linkage with 8 links and 9 simple revolute joints is

For a mechanism shown below, the mechanical advantage for the given configuration is

The lengths of the links of a 4-bar linkage with revolute pairs only are $$p,q,r$$ and $$s$$ units. Given that $$p < q < r < s.$$ Which of these links should be the fixed one, for obtaining a ‘double crank’ mechanism?