Answer:
21
Step-by-step explanation:
stage 1: 1
stage 2: 3
stage 3: 6
the pattern is that the number of squares increases everytime by the stage number it is. for example stage 2 has 3 squares. to find stage 3 you start off with 3 squares (from stage 2), and add the stage number (stage 3). 3+3=6 so stage 3 has 6 squares.
stage 4: 10 (6+4)
stage 5: 15 (10+5)
stage 6: 21 (15+6)
