A pin support will exert both horizontal and vertical components of reaction as the reaction forces. Members will be subjected to tensile or compressive forces which will act along the axis of the rods. The support at I is roller type. Thus, it will exert only the vertical component of reaction.
Moment of force about a point is determined as the product of force and its perpendicular distance from the point considered. It can be expressed as,
Here, moment is M, force is F and the perpendicular distance is d.
Consider the free body diagram of the given truss with components of reactions as shown.
From the free body diagram, apply equilibrium force equation in horizontal direction.