Question 1082288
In this case, we only have one equation with two variables.

Let B:  number of books purchased
    T:  number of toys purchased.

1)11B + 6T = 157 or B = (157-6T)/11

So we make a board with the possible values of T, until the other variable (B) is also an integer.

 if  T = 0 then B = 157/11 (not an integer)
 if  T = 1 then B = 151/11 (not an integer)
 if  T = 2 then B = 145/11 (not an integer)
 if  T = 3 then B = 139/11 (not an integer)
 if  T = 4 then B = 133/11 (not an integer)
 if  T = 5 then B = 127/11 (not an integer)
 if  T = 6 then B = 121/11 = 11.

Here we can continue, if we need another solution (if there is another one) or we can stop the procedure.

Answer: He bought eleven books and six toys.

@natolino_