Solve simultaneous equation x-y=4 and x²+y²=10​

The quadratic function h(t) = -16.1t^2 + 150 models a balls height, in feet, over time, in seconds, after its dropped from a 15 story building. from what height in feet was the ball dropped?

Naomi’s parents want to have 50,000, saved for her college education, if they invest 20000 today and earn 7% interest compound annually, about how long will it take them to save 50 thousand

Offering 30 if a plus b plus c equals 68 and ab plus bc plus ca equals 1121, where a, b, and c are all prime numbers, find the value of abc. the answer is 1978 but i need an explanation on how to get that.