we have
x ----> number of hats the sold
y ----> number of scarves they sold
so
12x+15y=690 ------> equation A
y=x+10 -----> equation B
Solve the system of equations
Using substitution Method
substitute equation B in equation A
12x+15(x+10)=690
solve for x
12x+15x+150=690
27x=690-150
27x=540
x=20
Find out the value of y
y=x+10
y=20+10
y=30
therefore
The answer is
20 hats and 30 scarves
