Here is the complete mapping from hex digits to decimal and binary:
0=0 (0000), 1=1 (0001), 2=2 (0010), 3=3 (0011), 4=4 (0100), 5=5 (0101), 6=6 (0110), 7=7 (0111), 8=8 (1000), 9=9 (1001), A=10 (1010), B=11 (1011), C=12 (1100), D=13 (1101), E=14 (1110), F=15 (1111).
Notice how each hex digit maps exactly to 4 bits. This makes hex-to-binary conversion instant: just replace each hex digit with its 4-bit pattern. For example, 3F in hex becomes 00111111 in binary.