3102 base4 = 3x4^3+ 1x4^2 + 2x1 = 3x64 + 1x16 + 2 = 210 base10
The powers of 2 are 2, 4, 8, 16, 32, 64, 128, 256
210 = 128 + 64 + 16 + 2 = 2^7 + 2^6 + 2^4 + 2^1 = 11010010 base2
A faster method is to each digit in base 4 to two digits in base 2
3 base4 = 11 base2
1 base4 = 01 base2
0 base4 = 00 base2
2 base4 = 10 base2
So 3102 base4 = 11010010 base2
If you wanted to convert base 4 to (say) base 5 you would need the first method and convert to base 10 first