Let m and s be the number of math and sociology books sold respectively.
m=s+88 we are also told that:
m+s=426, using m found above in this equation gives you:
s+88+s=426 combine like terms on left side
2s+88=426 subtract 88 from both sides
2s=338 divide both sides by 2
s=169, since m=s+88
m=169+88=257
So 257 math and 169 sociology textbooks were sold.
