Heres a tip---- if it has a square its 90 degrees if it doesnt its 180 and if its in an x shape theyre equal
First add up the total parts in the ratio.
5 + 4 = 9
Now we need to know the value of each part
36 / 9 = 4
The girls has total of 4 parts, therefore we can just multiply the number of parts by the amount in each part
4 x 4 = 16
So there r 16 girls in the class
2(5*4)+2(4*3)+2(3*5)=94 sq.m (Orginial SA)
2(4*5)+2(5*6)+2(6*4)=148 sq.m (Total SA)
148-94=54 (New SA)