4/5k + 7/10 = 13/15k - 3/5
4/5k - 13/15k = -3/5 - 7/10
12/15k - 13/15k = -6/10 - 7/10
-1/15k = - 13/10
k = -13/10 * - 15/1
k = 195/10 = 39/2 or 19.5
or this way
4/5k + 7/10 = 13/15k - 3/5....multiply everything by LCD of 30
24k + 21 = 26k - 18
24k - 26k = -18 - 21
-2k = - 39
k = 39/2 or 19.5