Let #D_I# be the distance traveled by Ian
Let #x# be Ian's speed.
Let #y# be the duration that Ian traveled
#D_I = xy#
Let #D_H# be the distance traveled by Han
#D_H = (x + 5)(y + 1)#
#=> D_H = xy + x + 5y + 5#
#D_H = xy + 70#
#xy + x + 5y + 5 = xy + 70#
#=> x + 5y + = 65#
Let #D_J# be the distance traveled by Jan
Let #Z# be the extra distance traveled by Jan compared to Ian
#D_J = (x + 10)(y + 2)#
#D_J = xy + Z#
#=> xy + 2x + 10y + 20 = xy + Z#
#=> 2x + 10y + 20 = Z#
#=> 2(x + 5y) + 20 = Z#
#=> 2(65) + 20 = Z#
#=> Z = 150#