Answer:
t = 0.77
Step-by-step explanation:
f(t) = 11 × (1.5^t)
f(t) = 15
11 × (1.5^t) = 15
1.5^t = 1.364 (3d.p)
log1.5(1.364) = t
t = 0.77 (2d.p)