Rashi on Exodus 5:8/רש"י על שמות ה׳:ח׳

1ואת מתכנת הלבנים means the total number of bricks which each made per day when straw was being supplied to them — that total you shall impose upon them now also, in order that the service may be hard upon them.

2כי נרפים signifies because they have loosened themselves from the work; therefore (this word in Rashi corresponds to על כן in the Hebrew text) their mind turns to idleness and they cry out, saying, נלכה וגו׳ LET US GO [AND SACRIFICE etc.].

3מתכנת — This word, and ותכן (v. 18), and the words of the same root in (I Samuel 2:3) “And by Him actions are counted (נתכנו)” and in (2 Kings 12:12) “the money that was counted (המתכן)”, all have the meaning of counting.

4נרפים — The work is loose (רפויה) in their hand and neglected by them so that they are loosened (הם נרפים) from it. In old French retrait.