Question 180041
Let B = the number of boys and G = the number of girls.
B+G = 26 "The number of students is 26"
The girls drew triangles, each of which has three sides, so the total number of sides from the triangles is: 3*G
The boys drew rectangles each of which has four sides, so the total number of sides from the rectangles is: 4*B
Now you can write two equations as follows:
1) B+G = 26 Rewrite this as: B = 26-G and substitute for B in equation 2).
2) 4*B+3*G = 92 which is the total number of sides. 
4(26-G)+3*G = 92 Simplify and solve for G.
104-4G+3G = 92 Subtract 104 from both sides.
-G = -12 Divide through by -1 to make positive.
G = 12
To find the number of boys (B):
B = 26-G
B = 26-12
B = 14
So the number of boys is 14 and the number of girls is 12
Check:
B+G = 26
14+12 = 26
26 = 26 OK!
4*B+3*G = 92
4*14+3*12 = 92
56+36 = 92
92 = 92 OK!