一道物理理解问答、计算题,英文版的,本人不大理解题目的意思,

一道物理理解问答、计算题,英文版的,本人不大理解题目的意思,
Figure below shows a uniform ruler of 120g is suspended at its midpoint from a spring balance which is calibrated in Newton(N).
A triangular block is suspended from the metre rule at the 25cm mark.It is balanced by a 250g mass suspended from the 75cm mark.[Take g=10N/kg.]
(a)Calculate the mass of the triangular block.
(b)Why the mass of the metre rule does not play a part in the calculation in (a)?
(c)What is the reading on the spring balance?

下图表示一个120g的尺子被悬挂在一个校准牛顿的秤的中央.
一个三角悬挂在尺子25cm处,同时在尺子75cm处,一个250G的“重量”（在这里,重量为名词）和三角保持着平衡.[用g=10n/kg]
a 三角的重量为?
250
b 为什么尺子的重量并不干扰计算?
because the calculation involves only the triangular block and the 250g mass,the weight of the ruler doesn't interfere with the weight of the triangular block.
c 上面那个称会显示什么（如果比较三角和250这个重量的话）
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