Calculate number of chips to solve bit commitment using hash function I have a problem that I don't know how to solve

Assume that H is a cryptographic hash function with output size 80 bits. Assume that ABC123 is a specifically designed line of hardware chips for computing H. where ABC123  can create 10000 hash values a second. This product line is the best, fastest and affordable, in the market, priced at 1000$. Consider the following Bit-Commitment protocol which is used for applications in betting in football matches.


A create R1 and R2 as 2 random binary strings with length 48 bits and 40 bits, respectively
A send host B: M = H(R1 || R2 || b) || R1
To announce bit b, A send host B: (R2, b) (b is a bit, 0 or 1, that A choose indicate that a football team win or lose, for simplify)
B check validity by re-hashing H(R1 || R2 || b) and comparing with the value received from step 2


Question: how much money the host B has to invest in order to correctly guess b in 5 minutes?

Thank you very much. Any help is appreciated!
$M = H(R_1 || R_2 || b) || R_1$

You already know $R_1$ and you need to find $R_2$ and $b$.

$R_2$ is 40 bits long and $b$ is 1 bit, so you need on average $2^{41}$ guesses to find $R_2$ and $b$ which will give the hash you want.

You know that each chip can do 10,000 hashes per second, so you need to find out how many chips you'll need to do $2^{41}$ hashes in 5 minutes.

$\dfrac{2^{41}}{300seconds} = 7,330,077,518.51 hashes/second$

Since each chip can peform 10,000 hashes per second, we need

$\dfrac{7,330,077,518.51}{10000} = 733,008$ chips (rounded up)

At \$1000 per chip, that is \$733,008,000