Returning a calculation result of local variable references

I'm trying to declare a struct with generics that implements some custom calculations. Generic type T might be a primitive or another bit large struct those implements operator overloads.

If the function calc has a single operation like below, it is compiled with no problems.

struct MyNumber<T> {
    a: T,
    b: T,
}

impl<'a, T> MyNumber<T> {
    pub fn calc(&'a self, other: &'a Self) -> T where &'a T: Add<&'a T, Output = T> {
        &self.a + &other.a
    }
}

But if the function has multiple operation with temporary variables, the compiler claims an error.

struct MyNumber<T> {
    a: T,
    b: T,
}

impl<'a, T> MyNumber<T> {
    pub fn calc(&'a self, other: &'a Self) -> T where &'a T: Mul<&'a T, Output = T> + Add<&'a T, Output = T> {
        let t1 = &self.a * &other.a;
        let t2 = &self.b * &other.b;
        &t1 + &t2
    }
}

Error message is:

error[E0597]: `t1` does not live long enough
  --> src/lib.rs:15:9
   |
11 | impl<'a, T> MyNumber<T> {
   |      -- lifetime `'a` defined here
12 |     pub fn calc(&'a self, other: &'a Self) -> T where &'a T: Mul<&'a T, Output = T> + Add<&'a T, Output = T> {
13 |         let t1 = &self.a * &other.a;
   |             -- binding `t1` declared here
14 |         let t2 = &self.b * &other.b;
15 |         &t1 + &t2
   |         ^^^------
   |         |
   |         borrowed value does not live long enough
   |         requires that `t1` is borrowed for `'a`
16 |     }
   |     - `t1` dropped here while still borrowed

I can't understand what these messages mean because it seems references of t1 and t2 makes a new variable (T) then t1 and t2 are no longer needed at the end of function.

Why this code is invalid? And how should I fix it?

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