Replace vowels with 1 and consonants with 0. you will get a binary string. For eg hello will become 01001.
Now the problem reduces to binary to decimal conversion.
Approach for binary to decimal conversion:
16 8 4 2 1
0 1 0 0 1
n = length of string
Initialize the answer to 0.
Iterate over the string
Whenever you get 1 in the binary string you need to calculate pow(2, n-i-1) , where i is the ith index from the start and add it to the answer.
At each step whenever there is 1 in the binary string you need to compute power of 2. Since this can be very large. we compute it modulo 109+7. For this we use modular exponentiation.