Answer
a. year $2016$
b. year $2020$
c. years after 2020.
d. years after 2016.
Work Step by Step
a. Use the formula for the interfaith marriage $I=\frac{1}{4}x+26$, for $I\gt 33$, we have $\frac{1}{4}x+26\gt 33$ which gives $\frac{1}{4}x\gt 7$ and $x\gt 28$. Thus the year should be $1988+28=2016$
b. Use the formula $N=\frac{1}{4}x+6$, for $N\gt 14$, we have $\frac{1}{4}x+6\gt 14$ which gives $\frac{1}{4}x\gt 8$ and $x\gt 32$. Thus the year should be $1988+32=2020$
c. Find the intersection of the above results, we get $x\gt 32$ which means years after 2020.
d. Find the union of the results in (a) and (b), we get $x\gt 28$ which means years after 2016.
