1.家校距离 = x
x/12 - x/16 = 15/60 + 15/60 = 0.5
x(1/12 - 1/16) = x/48 = 0.5
x = 24 km
2.甲每小时加工 x 个
甲比乙每小时多加工4个零件, 乙每小时加工 x-4 个
(x + x - 4)*6 + 5x = 350
12x + 5x - 24 = 350
17x = 374
x = 22
甲每小时加工 22 个, 乙每小时加工 18 个

3. 每人每天完成一项工程的 x.
(7*18)*x = 3/5
x = (3/5)/126 = 1/210
(1- 3/5)/[(18+3)*(1/210)] = 4
还要 4 天完成

4.甲乙的本钱和:x
120/(1+50%) + 120/(1-20%) = x
 x = 80 +150 = 230
 120*2-230 = 10
总共赚了 10 元

5.商品的标价: x
x * 0.8 - x * 0.6 = 20
x = 100
商品的进价 = x * 0.8 - 10 = 70