Crack The Safe - Formulae (Substitution and Rearranging)

Three “Crack The Safe” activities on formulae: substituting and two one rearranging (the second one is harder than the first, involving the subject appearing twice). These contain six questions but three possible answers for each question on the rearranging with there being ten possible answers for the six questions on the substitution; this means that students can self-check their answers (are they in the list of possible answers?) whilst the teacher can help those who require it. I use these as starters and plenaries but that is obviously up to you with the wrong answers offering an opportunity for discussion about what I have done in order to get that solution.