Brianne saves $10 x 2 = $<<10*2=20>>20 in February.
She will save $20 x 2 = $<<20*2=40>>40 in March.
She will save $40 x 2 = $<<40*2=80>>80 in April.
Therefore, she will save $80 x 2 = $<<80*2=160>>160 in May.
#### 160