x=cy , where c is a scalar
comparing , t+1=c ---1 , 3=c(t-1) --- 2 , solve them .
Since they are parallel , their gradients are equal .
gradient of x = 3/(t+1)
gradient of y = t-1
set them equal , and solve for t .
(Bold is to indicate sth is a vector , else it would be a variable)