Answer:
Simple. since we know the weight per given length, we simply need to know the total length of all steel used. the perimeter is easy as it is given, 2×12 and 2×5 for a total perimeter of 24+10 or 34m. now the diagonals must be calculated...
since this is a right triangle, one could easily use a trig function to calculate, but to keep it simple pathag. theorum a2+b2=c2, where the 2 means squared. rearrange to c=sqrt(a2+b2), or 12 squared + 5 squared...giving 144+25=169. then take square rt of 169. this is length of one diagonal, remember to multiply by 2 since there are two diagonal pieces. add this to total perimeter of 34m above.
now that total length is known, simply multiply by weight/m for total weight
**remember units, as problems become complex keeping up with units can help u know if you are using right solving methods, like in heat transfer, energy equations, etc.