Robi will save $8 x 2 = $<<8*2=16>>16 in April.
He will save $16 x 2 = $<<16*2=32>>32 in May.
He will save $32 x 2 = $<<32*2=64>>64 in June.
Hence, his total savings after 6 months will be $2 + $4 + $8 + $16 + $32 + $64 = $<<2+4+8+16+32+64=126>>126.
#### 126