看图列式 ![](http://tikupic.21cnjy.com/f1/cb/f1cbde1128378d2b8c9850bff96edff6.png)
{#blank#}1{#/blank#} + {#blank#}2{#/blank#} = {#blank#}3{#/blank#}
{#blank#}4{#/blank#} + {#blank#}5{#/blank#} = {#blank#}6{#/blank#}
{#blank#}7{#/blank#} - {#blank#}8{#/blank#} = {#blank#}9{#/blank#}
{#blank#}10{#/blank#} - {#blank#}11{#/blank#} = {#blank#}12{#/blank#}