Let x = the larger number
Let y = the smaller number

>>...the difference of two numbers is 49...<

That says the same as

    The larger minus the smaller equals 49, or
             x   -         y        =   49            

So the first equation is x - y = 49


>>...The larger number is 3 less than 5 times the smaller number...<<

Replace "the larger number" by x and "the smaller number" by y

>>...x is 3 less than 5 times y...<<

Replace "is" by "=" and "5 times y" by "5y"

>>...x = 3 less than 5y...<<

That means to make 5y less by subtracting 3 from it:

>>...x = 5y - 3...<<

So the answer is b.

Edwin