Bull Call Spread

Today is October $15,$ the continuously compounded interest rate is r $=5\%,$ and price of crude oil is S$0=$ $$55.$ By December, it is expected to increase by a factor d $=0\mathrm{.}9$ or u $=1\mathrm{.}1$ with equal probabilities. A bank makes a market in $50/60$ March bull call spreads$$ on crude oil. Specifically, if a bank$$s customer buys the bull spread, it is as if this client:

$1.$ buys one call on crude oil with strike $$50,2.$ sells one call on crude oil with strike $$60$

Both options are European and mature in December, precisely in $2$ months. There are no transaction costs.

$($a$)(4$ points$)$ What is the premium collected by the bank who shorts the bull call spread to a customer?

$($b$)(2$ points$)$ How does the bank hedge $($i$.$e$.,$ describe the bank$$s replicating strat$-$ egy, including its position in bonds.$)?$