Help Make this Word problem (math) into equation?

Question

In an individual retirement account valued at $53900 a couple has 500 shares of stock some in big bank corporations and some in safe savings. if big bank sells for $115 per share and save savings sells for $97 per share how many shares of each does the couple own? The back of the book says the answer is 300 share of big banks 200 of safe savings how?????

Answer 1

Number of big bank shares = x

Number of safe savings shares = y

total cost = big bank shares cost + safe savings shares cost

$53900 = $115x + $97y (first equation)

total number of shares = big bank shares + safe savings shares

500 = x + y

or

y = 500 - x

substitute 500-x for y in the first equation

53900 = 115x + 97(500-x)

53900 = 115x + 48500 - 97x

53900 - 48500 = 18x

5400 = 18x

x = 5400/18

x = 300 big bank shares

y = 500 - x

y = 500 - 300

y = 200 safe savings shares