Answer:
surface area of shape= 3*(area of the rectangle)+2*(area of the triangle), since it's a prism
area of rectangle= length*breadth= 15*5
= 75mm^2
area of triangle = 1/2* base * height= 1/2* 4.5 * 5
= 11.25mm^2
surface area = 3*75 + 2*11.25
= 225 + 22.5
= 247.5mm^2
hope it helps