lateral area is area of sides, not including base and top
if we look at it, that means just find the area of the 2 triangles and the small rectangle at the end becaseu the other 2 rectangles are base and top
areatriangle=1/2bh
arearectangle=bh
arearectangle=515=75
area triangle (there are 2 of them )=21/2512=60
total is 75+60=135 mm^2
