Grandma Wang’s water bill this month is the sum of water, gas and electricity (1/4), and the electricity bill is the gas bill (7/8). The water bill is 21 yuan less than the gas bill. How much is the water bill? ?
王奶奶家本月水费是水、煤气和电三项费用之和的(1/4)，电费是煤气费的(7/8)，水费比煤气费少21元，求水费多少元？
<gadget id="calculator">1 / 4</gadget>
<output>1/4 = around 0.25</output>

<gadget id="calculator">1 - (1/4)</gadget>
<output>3/4 = around 0.75</output>

<gadget id="calculator">7 / 8</gadget>
<output>7/8 = around 0.875</output>

<gadget id="calculator">1 + (7/8)</gadget>
<output>15/8 = around 1.875</output>

<gadget id="calculator">(3/4) / (15/8)</gadget>
<output>2/5 = around 0.4</output>

<gadget id="calculator">(2/5) - (1/4)</gadget>
<output>3/20 = around 0.15</output>

<gadget id="calculator">21 / (3/20)</gadget>
<output>140</output>

<gadget id="calculator">140 * (1/4)</gadget>
<output>35</output>

<result>35</result>