How do you work out the math problem (1+19:12) t-1

Well ...

you always do multiplication/division first (when parenthesis are involved, do what's in parentheses first following that same rule in this case)

19 : 12 can't be reduced to a whole number or a simplifies fraction so you're stuck with 19/12

1 + (19/12) = (12/12) + (19/12) = 31/12

This fraction also can't be reduced.

ok, so that's what's in the parentheses.

(31/12) t - 1

If you need to solve for t:

set equation to 0

(31/12) t - 1 = 0

(31/12) t = 1

(31/12) t • (12/31) = 1 • (12/31)

t = 12/31

Assuming it is (1+19:12) (t-1):

it is still (31/12)

(31/12) (t-1)

multiply the terms in the parenthesis:

(31t/12) - (31/12)

if solving for t:

set equation for 0 and do not multiply the terms together:

(31/12) (t-1) = 0

(12/31) • (31/12) (t-1) = 0 • (12/31)

multiplying anything by 0 is 0.

t-1 = 0

t=1