Because circle plus square equals 58, triangle plus circle equals 38, and triangle plus square equals 26.

So add them up first.

That is, 2 triangles +2 circles +2 squares =58+38+26= 122.

So triangle plus square plus circle = 122/2=6 1.

So triangle =6 1-58=3 circle =6 1-26=35 square =6 1-38=23.

Hope to adopt. thank you