Only using 1 2 3 4, find a solution that equals 18, 19, 20, and 21

See below, there may be more than one answer

Step-by-step explanation:

4(3+1)+2 = 18

(4+2)(3)+1 = 19

(1)(2+3)(4) = 20

(1+2)(3+4) = 21

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