You just need to subtract out the three checks that didn't clear on her last statement.
$324.18
($15.00)
($77.49)
($124.28)
________
$107.41 Total she should have had before her deposit
($487.38) Balance she had after her deposit
_______
$379.97 is how much of a deposit she made
The like terms in this expression would be the variables and the numbers without variables. This can be converted into:
And this is .
Let the required number be x, then 10 + x/6 = 5
x/6 = 5 - 10 = -5
x = 6 x -5 = -30
x = -30