Question 514934
From the data
let the seventeenth number be x and the 33rd number in the AP be y
x=a+(n-1)d
x=a+(17-1)d (since it is given n=17)
x=a+16d  
81=a+16d  (1)     (given 17th term is 81)
Also
y=a+(33-1)d
y=a+32d  
145=a +32d (2)    (given 33rd term is 145)

(1)-(2)

81-145=-16d
-64=-16d
d=4
From 1
81=a+16d
a=81-16*4
 =81-64
 =17